feat(webui): gated action framework (#434)

Register future write actions with task_capability_map metadata,
mutation-ledger previews, and fail-closed execution in the read-only MVP.
Adds /actions routes, disabled UI buttons, and tests proving ungated
attempts cannot invoke mutations.

Closes #434

docs/webui-local-dev.md

@@ -47,9 +47,12 @@ Optional environment variables:
 | `/audit` | Stub — report audit paste (#431) |
 | `/worktrees` | Stub — hygiene dashboard (#432) |
 | `/leases` | Stub — lease visibility (#433) |
+| `/actions` | Gated write-action registry — all disabled in MVP (#434) |
+| `/api/actions` | JSON action registry with capability metadata |
+| `/api/actions/{id}/preview` | Mutation ledger preview (GET, read-only) |
 
-All routes are GET-only. POST/PUT/PATCH/DELETE return `405` with
-`read-only-mvp`.
+All routes are GET-only except registered POST handlers, which still return
+`405` with `read-only-mvp` until write paths ship.
 
 ## Project registry (#427)
 
@@ -82,8 +85,17 @@ credentials. The UI surfaces pagination proof (returned count, pages fetched,
 If credentials are missing or the fetch fails, the page shows an explicit error
 instead of an empty queue (fail closed).
 
+## Gated actions (#434)
+
+`/actions` registers future write actions (claim, comment, review, merge,
+delete branch, create PR/issue). Each entry declares the MCP tool, required
+permission, and profile role from `task_capability_map.py` — aligned with
+`gitea_resolve_task_capability`. Buttons are disabled; previews always render
+a mutation ledger. Direct `attempt_action` calls fail closed without invoking
+MCP tools.
+
 ## Tests
 
 ```bash
-pytest tests/test_webui_skeleton.py tests/test_webui_project_registry.py tests/test_webui_prompt_library.py tests/test_webui_queue_dashboard.py -q
+pytest tests/test_webui_skeleton.py tests/test_webui_project_registry.py tests/test_webui_prompt_library.py tests/test_webui_queue_dashboard.py tests/test_webui_gated_actions.py -q
 ```