feat(templates,qa): template gallery + pluggable DocQA engine

Two more features from the deferred menu:

Daily-note template gallery:
- src/main/DailyNotesTemplates.js — pure module: listTemplates() /
  saveTemplate() / deleteTemplate() / labelFor() with injectable IO.
- src/main/DailyNotes.js — openOrCreate() now accepts seedContent so a
  non-default template can seed a NEW note (existing notes never get
  clobbered).
- src/main.js — IPC channels daily-templates:list / save / delete /
  apply. apply renders the chosen template (with {date}/{weekday}
  substitution) and pipes through DailyNotes.openOrCreate.
- src/sidebar/daily-templates-panel.js — gallery UI: list, +New
  (prompt for name + content), Use (applies to today's note),
  delete (refuses to remove the last template so the default survives).
- src/renderer.js — registers the panel.
- src/index.html — icon (already added).

Pluggable DocQA engine (semantic search hook):
- src/main/SemanticEngine.js — engine interface with defaultEngine() (TF-idF,
  always available) and neuralEngine() (lazy @xenova/transformers,
  falls back gracefully when the dep is missing). getEngine(name)
  resolves either.
- src/main/DocQA.js — ask() is now async and accepts an engine arg.
  TF-idF path unchanged; neural path calls engine.rank(question, chunks)
  directly. The chunk corpus is built up front regardless of engine so
  ranking is consistent.
- src/main.js — doc-qa:ask IPC resolves the engine via SemanticEngine.getEngine(name)
  before calling DocQA.ask. The renderer can pass {engine: 'transformers'}
  to opt in once @xenova/transformers is installed.

Tests (51 new across this batch):
- tests/main/DailyNotesTemplates.test.js (18): labelFor separators /
  edge cases / non-string safety, listTemplates empty / present / sort,
  saveTemplate nested dir + .md extension + validation + null content,
  deleteTemplate success / missing / validation.
- tests/daily-templates-panel.test.js (12): mount + empty state + list +
  XSS safety, Use button (apply + error path), Delete button (success +
  last-template guard), New template (save + cancel), refresh.
- tests/main/SemanticEngine.test.js (8): default engine shape + rank
  matches WorkspaceSearch, getEngine for tf-idf / unknown / transformers
  (graceful fallback when @xenova/transformers missing), parity check.
- DocQA: 5 new tests for engine arg (custom engine.rank called, default
  fallback, neural hit shape translation); existing tests updated to
  await the now-async ask().

Full suite: 76 suites, 914 tests, lint+format clean.

Activation for the neural engine:
  npm install @xenova/transformers
  (heavy; ~50 MiB with deps) — then 'transformers' is selectable in
  doc-qa:ask. Until then, all calls use TF-idF transparently.

Amit Haridas

src/renderer.js

@@ -2263,6 +2263,25 @@ document.addEventListener('DOMContentLoaded', async () => {
         onOpenFile: (filePath) => ipcRenderer.send('open-file-path', { path: filePath }),
       }),
   });
+
+  // Daily-note template gallery — list / create / apply / delete the .md
+  // templates in <userData>/notes/templates/. Picking one seeds today's
+  // note via daily-templates:apply.
+  sidebarManager.registerPanel('daily-templates', {
+    title: 'Daily Templates',
+    icon:
+      '<svg viewBox="0 0 24 24" width="16" height="16"><path fill="currentColor" d="M3 5a2 2 0 0 1 2-2h11l-2 2H5v12h14V9l2-2v11a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2V5zm5 0h2v2H8V5zm0 4h2v2H8V9zm0 4h2v2H8v-2z"/></svg>',
+    render: (container) =>
+      require('./sidebar/daily-templates-panel').renderDailyTemplatesPanel(container, {
+        listTemplates: () => ipcRenderer.invoke('daily-templates:list'),
+        saveTemplate: ({ name, content }) =>
+          ipcRenderer.invoke('daily-templates:save', { name, content }),
+        deleteTemplate: ({ name }) => ipcRenderer.invoke('daily-templates:delete', { name }),
+        applyTemplate: ({ templateName }) =>
+          ipcRenderer.invoke('daily-templates:apply', { templateName }),
+        onOpenFile: (filePath) => ipcRenderer.send('open-file-path', { path: filePath }),
+      }),
+  });
   sidebarManager.registerPanel('git', {
     title: 'Git',
     render: (container) =>