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_149.md

@@ -0,0 +1,28 @@
+# Task ID: 149
+
+**Title:** Task PR linkage and human accept gate
+
+**Status:** pending
+
+**Dependencies:** 130, 148
+
+**Priority:** high
+
+**Description:** Integrate GitProvider into TaskService for PR creation on push and merge on accept
+
+**Details:**
+
+Update src/mcpd/src/services/task.service.ts:
+1. linkPR(taskId, branch, headCommit): create PR via GitProvider, update Task with prUrl, prNumber
+2. accept(taskId, userId, note):
+   - Verify task is in awaiting_review state
+   - Check PR combined status is success (optional gate based on project config)
+   - Call gitProvider.mergePullRequest
+   - Transition to merged state
+   - Create TaskEvent
+3. If merge fails, keep in awaiting_review, surface error
+4. reject: transition to in_progress, clear PR linkage or keep for reference
+
+**Test Strategy:**
+
+Unit tests: test linkPR updates task fields, test accept calls merge API, test accept fails if PR status is failing.