feat(sdk): contributes.skills — skills IdeA-native déclarables par plugin — #282 (types IdeAPluginSkillContribution/IdeAPluginSkillKind: id/name/description/kind workflow|reference/path .md package-relative, validation manifeste, export public; docs manifest + codex-skills-and-idea-plugins recentrés skills IdeA-native vs .codex-plugin Codex, README; QA verte: npm run build)

docs/manifest.md

@@ -143,6 +143,40 @@ development loop.
 
 ## Contributions
 
+`contributes.skills` declares read-only agent skills shipped inside the IdeA
+plugin package. These skills are IdeA-native: IdeA can expose them in project
+plugin settings, assign them to agents, inject them into the agent skill
+catalogue, and serve their Markdown body through `idea_skill_read` for every
+supported harness that receives IdeA capabilities, including Claude Code,
+Codex, OpenCode local and OpenCode cloud.
+
+```json
+{
+  "contributes": {
+    "skills": [
+      {
+        "id": "unity.build-debug",
+        "name": "unity-build-debug",
+        "description": "Diagnose Unity build failures.",
+        "kind": "workflow",
+        "path": "skills/unity-build-debug/SKILL.md"
+      }
+    ]
+  }
+}
+```
+
+Skill contribution rules:
+
+- `id` is stable within the plugin and is used by project/agent assignments.
+- `name` is the agent-facing name shown in the injected skill catalogue and
+  accepted by `idea_skill_read`.
+- `description` is the short affordance shown before the agent loads the skill.
+- `kind` defaults to `"workflow"`; `"reference"` is also supported.
+- `path` must be a package-relative Markdown file path ending in `.md`.
+- Installing a plugin globally is not enough: a project must enable the plugin,
+  then assign the skill to the target agent.
+
 `contributes.layouts` is the only surface for plugin layouts. The same layout
 contribution can be mounted inside an IdeA layout cell or opened in a detached OS
 window. Do not add a separate manifest contribution type for windows.