icon: Inkwell's mark is a black inkpot and quill on the brand yellow

Step 5 of milestone 481. Replaces the linked-notes constellation, which had been
stale since note links were dropped (alembic 0024). The colour scheme stays.

packaging/icons.py draws the mark once and renders every variant from it: the
rounded tile (web, desktop), the maskable full-bleed web icon, and the Android
adaptive foreground. The detail (shaft, vane splits, glint) is cut out of the ink
with a mask rather than painted on in yellow, because the Android foreground is
now transparent and its alpha is also the themed-icon silhouette. The old
foreground was the opaque maskable tile, which a themed icon would have drawn as
a solid square.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

desktop/README.md

@@ -45,13 +45,14 @@ cd desktop/src-tauri && cargo tauri dev
 ## Build (Linux)
 
 ```sh
-cargo tauri icon "$(git rev-parse --show-toplevel)/frontend/public/icon.svg"
 cd desktop/src-tauri && cargo tauri build   # -> .deb + .AppImage
 ```
 
-App icons are **generated** from the frontend's `icon.svg` via `cargo tauri icon`
-(not committed; CI does this before `cargo tauri build`). Bundle targets: `deb`,
-`appimage` (Linux-first; Windows/macOS later, no code changes expected).
+App icons are **generated and committed**: `python3 packaging/icons.py` draws the
+inkwell mark once and renders every web, desktop and Android icon from it,
+including `app-icon.png` and `icons/*.png` here. The Windows lane derives its
+`.ico` from `app-icon.png` with `cargo tauri icon` at build time. Bundle targets:
+`deb`, `appimage` (Linux-first; Windows/macOS later, no code changes expected).
 
 ## Status