fix(plugins): isole les menus plugin et durcit hello-plugin SDK contre la rechute #120

Requalification Architect du 2026-08-01: le crash INTERFACE INTERROMPUE au
chargement d'un plugin (menu + item) remonte via ProjectsView -> usePluginMenus
-> MenuBar jusqu'à RootErrorBoundary, quel que soit le plugin (ancien ou
reconstruit via SDK).

- usePluginMenus isole la résolution/conversion des contributions plugin :
  toute erreur retombe sur [] au lieu de propager.
- ProjectsView sépare les menus natifs des menus enrichis par plugin et rend
  MenuBar derrière une error boundary locale (fallback menus natifs seuls).
- hello-plugin (SDK) et les tests d'installation associés durcis en cohérence.

Bookkeeping ticket #120 uniquement (issue.md, carnet.md) ; les fichiers
counter.json/index.json et le dossier tickets/122/ restent hors commit car
une collision de numérotation #122 existe entre cette base et
feature/ticket120-hello-plugin-install-path-audit (deux tickets différents
revendiquent #122) — à arbitrer avant de committer le bookkeeping global.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

sdk/IdeaSDK/examples/hello-plugin/README.md

@@ -1,6 +1,13 @@
 # Hello Plugin
 
-Minimal IdeA plugin example using the public SDK types.
+Installable IdeA plugin example rebuilt from the public SDK types.
+
+It exercises the current plugin primitives end to end:
+
+- top-level menu: `Hello Plugin`;
+- menu entry: `hello-plugin`;
+- command: `hello-plugin`, returning `hello-world`;
+- layout contribution: `hello-plugin.hello-world`, rendered as `hello-world`.
 
 ```sh
 npm run typecheck:examples
@@ -10,3 +17,15 @@ npm run package:hello-plugin
 The installable archive is emitted at `examples/hello-plugin/build/hello-plugin-0.1.0.zip`.
 It contains `idea-plugin.json` at the ZIP root and the compiled ESM entrypoint at
 `dist/index.js`, matching the manifest `main` field.
+
+## Diagnostics
+
+During activation the plugin logs:
+
+- whether the command and layout runtime registries are available;
+- successful registration of the `hello-plugin` command;
+- successful registration of the `hello-plugin.hello-world` layout;
+- the first layout render, including project/node identifiers.
+
+These messages are intentionally small and stable so installation, bundle import, activation and
+layout rendering failures can be separated quickly in IdeA logs/devtools.