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_068.md

@@ -0,0 +1,58 @@
+# Task ID: 68
+
+**Title:** Add integration tests for prompt links
+
+**Status:** done
+
+**Dependencies:** 57 ✓, 58 ✓
+
+**Priority:** medium
+
+**Description:** Create end-to-end integration tests for prompt link creation, resolution, and dead link detection.
+
+**Details:**
+
+1. Add tests in `/src/mcplocal/tests/integration/prompt-links.test.ts`:
+   ```typescript
+   describe('Prompt Links Integration', () => {
+     describe('link creation', () => {
+       it('creates link with RBAC permission', async () => {
+         // Setup: user with edit permission on target project
+         const prompt = await api.post('/api/v1/prompts', {
+           name: 'linked-prompt',
+           content: '[Link]',
+           projectId: targetProject.id,
+           linkTarget: 'source-project/server:uri'
+         });
+         expect(prompt.linkTarget).toBe('source-project/server:uri');
+       });
+       
+       it('rejects link creation without RBAC permission', async () => { ... });
+     });
+     
+     describe('link resolution', () => {
+       it('fetches content from source server', async () => { ... });
+       it('uses service account for RBAC', async () => { ... });
+     });
+     
+     describe('dead link lifecycle', () => {
+       it('detects dead link when source unavailable', async () => {
+         // Kill source server
+         const prompts = await api.get('/api/v1/prompts');
+         const linked = prompts.find(p => p.linkTarget);
+         expect(linked.linkStatus).toBe('dead');
+       });
+       
+       it('recovers when source restored', async () => { ... });
+     });
+   });
+   ```
+
+**Test Strategy:**
+
+This task IS the test implementation. Verify:
+- RBAC tests cover permission scenarios
+- Resolution tests verify content fetched
+- Dead link tests cover full lifecycle
+- Tests properly mock/control source servers
+- Tests clean up resources