merge: AgentProject membership — the junction is now load-bearing

Merges feat/agent-project-membership (task 166/152). An agent can finally join
many projects: membership routes, per-membership role and optional brain
override, chat resolving context from the membership, and CLI attach-agent /
detach-agent / get memberships. The legacy Agent.projectId fallback is kept for
this release as the schema comment promises.

Conflict resolved in main.ts: that branch added its RBAC case to
mapUrlToPermission inline, while this branch had extracted the function to
middleware/url-permission.ts so it could be tested. Kept the extraction and
ported the case into it — joining a team is `edit:agents:<name>`, not
`create:agents`, which is the authority to mint a whole agent.

Also fixes something the extraction makes possible. security.test.ts contained a
hand-copied reproduction of mapUrlToPermission, because main.ts self-invokes
main() and nothing in it was importable. A security test asserting against a
copy stops testing the system the moment the real one changes, and this copy had
already drifted. It now imports the real function; all 18 assertions still pass,
against the code that actually runs.

Local: build clean, workspace 2550 passed, lint unchanged at 794 errors.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N4wNHWf7xSwnZCWpJcyv9p

.taskmaster/tasks/task_151.md

@@ -0,0 +1,28 @@
+# Task ID: 151
+
+**Title:** Git webhook receiver for post-merge failure
+
+**Status:** pending
+
+**Dependencies:** 130, 148
+
+**Priority:** medium
+
+**Description:** Create webhook endpoint that reopens tasks when post-merge CI fails
+
+**Details:**
+
+Create src/mcpd/src/routes/webhook.routes.ts:
+1. POST /api/v1/webhooks/git/:provider - receive webhook payloads
+2. Validate webhook signature using provider-specific method (Gitea uses HMAC-SHA256 with secret)
+3. Parse payload to identify: repo, commit SHA, status (success/failure/pending)
+4. If status is failure for a merged commit:
+   - Find Task with that headCommit and state=merged
+   - Call taskService.reopenOnPostMergeFailure(taskId)
+   - This transitions merged→reopened and creates TaskEvent
+5. Register route in main.ts
+6. Webhook secret stored in CodeRepo's credential secret
+
+**Test Strategy:**
+
+Unit tests: test signature validation, test payload parsing, test reopen triggered on failure status. Integration: simulate Gitea webhook payload.