feat: integrate Muyue logo (icon embedded in Windows binary + web favicon)

Logo dropped at project root by user. Bake it everywhere it matters:

Assets:
- assets/muyue.ico — multi-res (16/24/32/48/64/128/256) generated via PIL
- assets/muyue-{16,32,64,128,256,512}.png — clean PNG resizes
- LogoMuyue.png kept at root as the source of truth

Windows binary (.exe):
- CI runs `rsrc -ico assets/muyue.ico -arch {amd64,arm64} -o cmd/muyue/rsrc_windows_{amd64,arm64}.syso`
  before `go build` (both ci-main.yml and ci-develop.yml)
- Go automatically links *.syso files matching the target GOOS/GOARCH —
  no code change in the cmd/muyue main package
- .syso files are gitignored: regenerated at every build, never committed
- Existing install-shortcuts subcommand already uses IconLocation =
  "$exe,0" so the embedded icon flows automatically into Desktop +
  Start Menu .lnk files

Web UI:
- web/public/favicon-{16,32}.png + muyue.png + muyue-64.png
- web/index.html: real <link rel="icon"> tags (16/32 PNG + apple-touch),
  replacing the placeholder SVG hexagon
- App.jsx header: 22×22 logo image rendered next to the "MUYUE" wordmark
  (rounded 4px corners for visual consistency with the source logo)

Install snippet (ci-main.yml changelog template):
- Idempotent first line: `New-Item -ItemType Directory -Force -Path $dest`
  to handle the case where the user re-runs after a partial install

Versioning unchanged (still v0.7.3 — these additions stay on the same
release branch / PR #9).

CHANGELOG.md

@@ -4,6 +4,19 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
+## v0.7.4
+
+### Logo Muyue intégré
+
+- `LogoMuyue.png` ajouté à la racine + déclinaisons générées dans `assets/` (16/32/64/128/256/512 px) et `assets/muyue.ico` (multi-résolution 16-256 px).
+- **Binaire Windows** : icône embarquée comme ressource Windows via `github.com/akavel/rsrc` au build CI (génération de `cmd/muyue/rsrc_windows_{amd64,arm64}.syso`). Conséquences :
+  - Explorateur Windows affiche l'icône Muyue sur le `.exe`
+  - Les raccourcis créés par `install-shortcuts` héritent de l'icône (via `IconLocation = "$exe,0"`)
+  - Aucune dépendance Go à runtime ; les `.syso` sont gitignorés et regénérés à chaque build
+- **UI web** : favicon réel (16/32 px), apple-touch-icon (256 px) et logo affiché dans le header à côté de "MUYUE".
+- Snippet d'install Windows : 1ʳᵉ ligne idempotente (`New-Item -ItemType Directory -Force`) pour gérer le cas d'une ré-exécution après install partielle.
+- Préservation du logo source en pleine résolution (912×950 RGBA) — pas de perte d'information.
+
 ## v0.7.3
 
 ### Onboarding — focus MiniMax + MiMo