fix(modals): drop shadcn-style aria-describedby to silence Radix warning

Every DialogContent had aria-describedby="X-desc" and every
DialogDescription had a matching id="X-desc". That pattern is the
default shadcn/ui recipe, but it breaks Radix 1.1.x.

Root cause: Radix auto-generates a descriptionId via useId() (e.g. :r0:)
and stores it in the Dialog context. The DescriptionWarning effect does
`document.getElementById(descriptionId)` and warns if the element is
missing. When the description element's id is overridden to
"welcome-desc", the DOM has id="welcome-desc" but the context still has
:r0:, so the lookup misses and the warning fires on every dialog open.

Fix: drop both overrides. Let Radix manage the id and aria-describedby
itself. Screen-reader semantics are unchanged (Radix still wires
Content -> Description via the auto-generated id).

Touched: 12 modal files (11 DialogContent/DialogDescription pairs +
SettingsSheet which uses Sheet). +1 regression test in
WelcomeDialog.test.tsx that spies on console.warn and asserts the
"Missing Description" message is never emitted.

Tests: 306/306 pass (was 305).

Long-term memory: radix-aria-describedby-anti-pattern.md captures the
do-not-reintroduce rule for future agents.

src/renderer/components/modals/AboutDialog.tsx

@@ -17,10 +17,10 @@ export function AboutDialog() {
 
   return (
     <Dialog open={isOpen} onOpenChange={(o) => !o && closeModal()}>
-      <DialogContent aria-describedby="about-desc">
+      <DialogContent>
         <DialogHeader>
           <DialogTitle>About MarkdownConverter</DialogTitle>
-          <DialogDescription id="about-desc">
+          <DialogDescription>
             Professional Markdown editor and universal file converter.
           </DialogDescription>
         </DialogHeader>

src/renderer/components/modals/AsciiGeneratorDialog.tsx

@@ -33,10 +33,10 @@ export function AsciiGeneratorDialog() {
 
   return (
     <Dialog open onOpenChange={(o) => !o && closeModal()}>
-      <DialogContent aria-describedby="ascii-desc" className="max-w-2xl">
+      <DialogContent className="max-w-2xl">
         <DialogHeader>
           <DialogTitle>ASCII generator</DialogTitle>
-          <DialogDescription id="ascii-desc">Type text, pick a font, see ASCII art</DialogDescription>
+          <DialogDescription>Type text, pick a font, see ASCII art</DialogDescription>
         </DialogHeader>
         <div className="space-y-3">
           <div>

src/renderer/components/modals/ConfirmDialog.tsx

@@ -17,10 +17,10 @@ export function ConfirmDialog(props: ConfirmProps) {
 
   return (
     <Dialog open onOpenChange={(o) => !o && handleCancel()}>
-      <DialogContent aria-describedby="confirm-body">
+      <DialogContent>
         <DialogHeader>
           <DialogTitle>{title}</DialogTitle>
-          <DialogDescription id="confirm-body">{body}</DialogDescription>
+          <DialogDescription>{body}</DialogDescription>
         </DialogHeader>
         <DialogFooter>
           <Button variant="ghost" onClick={handleCancel}>

src/renderer/components/modals/ExportBatchDialog.tsx

@@ -37,10 +37,10 @@ export function ExportBatchDialog({ sourcePaths }: { sourcePaths: string[] }) {
 
   return (
     <Dialog open onOpenChange={(o) => !o && closeModal()}>
-      <DialogContent aria-describedby="batch-desc">
+      <DialogContent>
         <DialogHeader>
           <DialogTitle>Batch export</DialogTitle>
-          <DialogDescription id="batch-desc">{sourcePaths.length} files</DialogDescription>
+          <DialogDescription>{sourcePaths.length} files</DialogDescription>
         </DialogHeader>
         <div className="space-y-3 text-sm">
           <div>

src/renderer/components/modals/ExportDocxDialog.tsx

@@ -41,10 +41,10 @@ export function ExportDocxDialog({ sourcePath }: { sourcePath: string }) {
 
   return (
     <Dialog open onOpenChange={(o) => !o && closeModal()}>
-      <DialogContent aria-describedby="docx-desc">
+      <DialogContent>
         <DialogHeader>
           <DialogTitle>Export to DOCX</DialogTitle>
-          <DialogDescription id="docx-desc">{sourcePath}</DialogDescription>
+          <DialogDescription>{sourcePath}</DialogDescription>
         </DialogHeader>
         <div className="space-y-3 text-sm">
           <div>

src/renderer/components/modals/ExportHtmlDialog.tsx

@@ -43,10 +43,10 @@ export function ExportHtmlDialog({ sourcePath }: { sourcePath: string }) {
 
   return (
     <Dialog open onOpenChange={(o) => !o && closeModal()}>
-      <DialogContent aria-describedby="html-desc">
+      <DialogContent>
         <DialogHeader>
           <DialogTitle>Export to HTML</DialogTitle>
-          <DialogDescription id="html-desc">{sourcePath}</DialogDescription>
+          <DialogDescription>{sourcePath}</DialogDescription>
         </DialogHeader>
         <div className="space-y-3 text-sm">
           <label className="flex items-center gap-2">

src/renderer/components/modals/ExportPdfDialog.tsx

@@ -56,10 +56,10 @@ export function ExportPdfDialog({ sourcePath }: { sourcePath: string }) {
 
   return (
     <Dialog open onOpenChange={(o) => !o && closeModal()}>
-      <DialogContent aria-describedby="pdf-desc">
+      <DialogContent>
         <DialogHeader>
           <DialogTitle>Export to PDF</DialogTitle>
-          <DialogDescription id="pdf-desc">{sourcePath}</DialogDescription>
+          <DialogDescription>{sourcePath}</DialogDescription>
         </DialogHeader>
         <div className="space-y-3 text-sm">
           <div>

src/renderer/components/modals/FindInFilesDialog.tsx

@@ -47,10 +47,10 @@ export function FindInFilesDialog() {
 
   return (
     <Dialog open onOpenChange={(o) => !o && closeModal()}>
-      <DialogContent aria-describedby="find-desc" className="max-w-2xl">
+      <DialogContent className="max-w-2xl">
         <DialogHeader>
           <DialogTitle>Find in files</DialogTitle>
-          <DialogDescription id="find-desc">
+          <DialogDescription>
             {rootPath ? `Search in ${rootPath}` : 'No folder open'}
           </DialogDescription>
         </DialogHeader>

src/renderer/components/modals/SettingsSheet.tsx

@@ -15,10 +15,10 @@ export function SettingsSheet() {
 
   return (
     <Sheet open onOpenChange={(o) => !o && closeModal()}>
-      <SheetContent aria-describedby="settings-desc" side="right" className="w-full sm:max-w-[480px]">
+      <SheetContent side="right" className="w-full sm:max-w-[480px]">
         <SheetHeader>
           <SheetTitle>Settings</SheetTitle>
-          <SheetDescription id="settings-desc">Editor, theme, and export preferences</SheetDescription>
+          <SheetDescription>Editor, theme, and export preferences</SheetDescription>
         </SheetHeader>
         <Tabs defaultValue="editor" className="mt-4">
           <TabsList className="grid w-full grid-cols-5">

src/renderer/components/modals/TableGeneratorDialog.tsx

@@ -60,10 +60,10 @@ export function TableGeneratorDialog() {
 
   return (
     <Dialog open onOpenChange={(o) => !o && closeModal()}>
-      <DialogContent aria-describedby="table-desc" className="max-w-2xl">
+      <DialogContent className="max-w-2xl">
         <DialogHeader>
           <DialogTitle>Table generator</DialogTitle>
-          <DialogDescription id="table-desc">Specify rows × columns to generate a markdown table</DialogDescription>
+          <DialogDescription>Specify rows × columns to generate a markdown table</DialogDescription>
         </DialogHeader>
         <div className="space-y-3">
           <div className="flex gap-3">

src/renderer/components/modals/WelcomeDialog.tsx

@@ -17,10 +17,10 @@ export function WelcomeDialog() {
 
   return (
     <Dialog open onOpenChange={(o) => !o && handleClose()}>
-      <DialogContent aria-describedby="welcome-desc" className="max-w-xl">
+      <DialogContent className="max-w-xl">
         <DialogHeader>
           <DialogTitle>Welcome to MarkdownConverter</DialogTitle>
-          <DialogDescription id="welcome-desc">
+          <DialogDescription>
             A polished editor for Markdown, with PDF, DOCX, and HTML export.
           </DialogDescription>
         </DialogHeader>

src/renderer/components/modals/WordExportDialog.tsx

@@ -65,10 +65,10 @@ export function WordExportDialog({ sourcePath }: { sourcePath: string }) {
 
   return (
     <Dialog open onOpenChange={(o) => !o && closeModal()}>
-      <DialogContent aria-describedby="word-desc">
+      <DialogContent>
         <DialogHeader>
           <DialogTitle>Export to Word (.docx)</DialogTitle>
-          <DialogDescription id="word-desc">{sourcePath}</DialogDescription>
+          <DialogDescription>{sourcePath}</DialogDescription>
         </DialogHeader>
         <div className="space-y-3 text-sm">
           <div>