fix(plugin-sdk): aligne le manifeste hello-plugin sur le schéma backend + fixture de test

Le manifeste hello-plugin était généré par un SDK obsolète/désaligné avec le
schéma backend actuel (champ ideaPluginManifestVersion manquant, displayName,
trustLevel, shape de contributes), ce qui faisait échouer l'installation avec
« invalid input: missing field ideaPluginManifestVersion ».

- SDK (manifest.ts/js, index.ts) aligné sur le schéma backend courant.
- hello-plugin (exemple + fixture) régénéré avec le manifeste valide.
- Base de tests fonctionnels plugins : fixture réelle versionnée
  (reference-minimal) + test d'installation/chargement bout en bout
  (plugin_install_load.rs), pour couvrir install/load/catalog depuis un
  dossier fixture réel.

Le sous-repo git imbriqué et vide (sdk/IdeaSDK/.git, 0 commit) a été
neutralisé pour que les sources du SDK soient suivies normalement dans ce
dépôt plutôt que comme gitlink vide.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

sdk/IdeaSDK/README.md

@@ -0,0 +1,84 @@
+# IdeA Plugin SDK
+
+Minimal public TypeScript SDK for IdeA plugins.
+
+This first version intentionally stays small:
+
+- public manifest types for `idea-plugin.json`;
+- public runtime types for plugin modules exposing `activate(ctx)`;
+- a lightweight manifest validator;
+- a minimal `examples/hello-plugin` plugin.
+
+## Install
+
+```sh
+npm install
+```
+
+## Build
+
+```sh
+npm run build
+```
+
+## Typecheck the example
+
+```sh
+npm run typecheck:examples
+```
+
+## Build the installable hello plugin archive
+
+```sh
+npm run package:hello-plugin
+```
+
+The archive is written to:
+
+```text
+examples/hello-plugin/build/hello-plugin-0.1.0.zip
+```
+
+Its ZIP root contains `idea-plugin.json` directly, with no wrapping parent directory. The
+compiled ESM entrypoint is emitted at `dist/index.js`, matching the manifest `main` field.
+
+## Plugin shape
+
+An IdeA plugin ships an `idea-plugin.json` manifest and a JavaScript entrypoint built from
+TypeScript.
+
+```json
+{
+  "ideaPluginManifestVersion": 1,
+  "id": "com.example.hello",
+  "displayName": "Hello Plugin",
+  "version": "0.1.0",
+  "main": "dist/index.js",
+  "trustLevel": "full",
+  "contributes": {}
+}
+```
+
+The entrypoint exports an `activate(ctx)` function:
+
+```ts
+import type { ActivateContext } from "@idea/plugin-sdk";
+
+export function activate(ctx: ActivateContext): void {
+  ctx.logger.info("hello from plugin");
+}
+```
+
+## Manifest Validation
+
+```ts
+import { validatePluginManifest } from "@idea/plugin-sdk";
+
+const result = validatePluginManifest(manifestJson);
+if (!result.success) {
+  console.error(result.errors);
+}
+```
+
+This validator is deliberately strict for core fields and permissive about future unknown fields.
+It is not a security boundary.