feat(flowchart): discoverable connect form + per-node color + save-to-file export; v4.12.0

User feedback on v4.11.0: the Add Connection form was buried below the
node/edge lists and they couldn't find it; they also asked for per-node
color and Save to File export. v4.12.0 reorganises the #fc-nodelist panel
to put the connect form right after the Add Node buttons, adds a native
<input type="color"> per node row that drives a new store.setNodeColor
mutator (with serialize/deserialize round-trip), and wires a Save to File
button that pops a system save dialog via a new 'save-text-file' IPC
channel.

- src/flowchart-generator.html — panel order is now Add Node /
  Add Connection / Nodes / Edges / Export (Insert · Save · Reset).
  Removed the legacy top toolbar; status moved into the panel.
  Added .fc-help, per-node color-picker CSS, .fc-toolbar-row.
- src/flowchart/flowchart-shapes.js — shapeSvg() accepts an optional
  6th 'color' arg; emits fill=... on rects and polygons. Falls back to
  #ffffff for empty/null/undefined so old callers keep working.
- src/flowchart/flowchart-store.js — setNodeColor(id, color) mutator
  with snapshot/emit, normalizeColor() helper (hex validation),
  addNode accepts color, deserialize normalises missing color.
- src/renderer/flowchart-bundle.js — mirrors all of the above inline
  (the bundle is loaded as a single <script>), wires fc-btn-save to
  api.saveFile, passes node.color to shapeSvg in the canvas render,
  and renders <input type='color'> per node row.
- src/main.js — new ipcMain.handle('save-text-file', ...) using a
  system Save dialog (mirrors the ascii:save handler shape).
- src/preload.js — added 'save-text-file' to ALLOWED_SEND_CHANNELS
  and a saveFile(content, defaultName) helper on the flowchart bridge.

Tests: 92/92 suites, 1165/1165 tests pass on this run
- +9 store tests (color defaults, setNodeColor, undo, hex validation,
  round-trip, deserialize normalisation)
- +7 shapes tests (fill color on all 5 kinds, fallback to #ffffff)
- +6 controller tests (color picker wires setNodeColor, canvas rect
  reflects color, Save to File calls api.saveFile with the fenced
  Mermaid source and 'flowchart.mmd', cancel + error paths surface in
  status)

Verification:
- npm run lint          clean
- npm run format:check  clean
- npm test              92/92 suites, 1165/1165 tests pass

Amit Haridas

UPDATES.md

@@ -1,5 +1,21 @@
 # PanConverter - Updates & Changelog
 
+## Version 4.12.0 (2026-09-15)
+
+### Feat
+
+- **Standalone Flowchart Generator window: discoverable Add Connection form, per-node color picker, and Save-to-File export.**
+  - **Reorganised the `#fc-nodelist` panel.** User feedback on v4.11.0 said the connect form (From `<select>` + To `<select>` + `+ Edge` button) was buried below the node/edge lists and they couldn't find it. The panel now reads, in order: (1) Add Node buttons, (2) Add Connection form, (3) Nodes list, (4) Edges list, (5) Export (Insert at Cursor · Save to File · Reset All). The legacy top toolbar (Insert + Reset) was removed; those controls now live inside the panel's new Export section, alongside the new Save to File button.
+  - **Per-node fill color.** Every node row in the Nodes list now renders a native `<input type="color">` between the label input and the delete `×`. Dragging through the picker fires `input` events that call the new `store.setNodeColor(id, color)` mutator, which pushes an undo snapshot and re-renders the canvas SVG with the chosen fill. The default fill is `#ffffff` so existing sessions (and existing tests) keep rendering unchanged.
+  - **`shapeSvg` accepts an optional color arg.** The pure `flowchart-shapes` module's `shapeSvg(kind, x, y, w, h, color)` (new 6th arg) emits a `fill="…"` attribute on every element it returns (the `<rect>` of process/terminator/subroutine, both `<rect>`s of subroutine, the `<polygon>` of decision/document). Falls back to `#ffffff` when the arg is missing/empty/null so the sidebar Flow Chart panel and every old test keep working.
+  - **`flowchart-store.setNodeColor` + persistence.** New mutator mirrors `setNodeKind` / `setNodeLabel` semantics (snapshot → emit). `addNode` now accepts an optional `color`. `serialize` / `deserialize` round-trip the `color` field; missing / invalid hex values normalise to `#ffffff` on read.
+  - **Save to File.** A new `Save to File` button next to `Insert at Cursor` calls `api.saveFile(fenced, 'flowchart.mmd')`, which invokes a new `save-text-file` IPC channel. The main-process handler (`src/main.js`) shows a system save dialog with `.mmd` / `.md` / `.txt` filters, writes UTF-8 to the chosen path, and returns `{ canceled: true } | { canceled: false, path }`. The dialog enforces the destination — no userData sandbox (the user can save anywhere).
+  - **`src/preload.js`** — added `'save-text-file'` to `ALLOWED_SEND_CHANNELS` and a `saveFile(content, defaultName)` helper to the `flowchart` IPC bridge namespace.
+  - **22 new tests:**
+    - `tests/flowchart-store.test.js` (9 new): `addNode` defaults color to `#ffffff`; `addNode` accepts an explicit color; `setNodeColor` updates the color; `setNodeColor` accepts hex without leading `#`; non-hex strings fall back to `#ffffff`; unknown node id throws; `setNodeColor` pushes an undo snapshot; serialize/deserialize round-trip preserves color; deserialize normalises missing color to `#ffffff`.
+    - `tests/flowchart-shapes.test.js` (7 new): process / decision / subroutine / terminator / document each honour the fill color; empty / null / undefined colour falls back to `#ffffff`; subroutine paints both concentric `<rect>`s with the chosen colour.
+    - `tests/flowchart-controller.test.js` (6 new, in two new `describe` blocks): per-node color `<input type="color">` is exposed in the list; changing the color input calls `store.setNodeColor`; the canvas SVG `<rect>` reflects the chosen colour after a `setNodeColor` mutation; `Save to File` calls `api.saveFile` with the Mermaid-fenced source and `'flowchart.mmd'`; cancel / error paths surface in `#fc-status`.
+
 ## Version 4.11.1 (2026-09-15)
 
 ### Chore