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_053.md

@@ -0,0 +1,54 @@
+# Task ID: 53
+
+**Title:** Add prompt index to initialize instructions
+
+**Status:** done
+
+**Dependencies:** 47 ✓, 44 ✓
+
+**Priority:** high
+
+**Description:** Modify the initialize handler to include the compact prompt index and gate message in instructions for gated projects.
+
+**Details:**
+
+1. Update initialize handling in `/src/mcplocal/src/router.ts`:
+   ```typescript
+   async handleInitialize(sessionId: string): Promise<InitializeResult> {
+     const state = this.getSessionState(sessionId);
+     
+     let instructions = this.projectConfig.prompt || '';
+     
+     if (state.gated) {
+       // Add gate instructions
+       const gateInstructions = await this.getSystemPrompt('gate-instructions');
+       
+       // Build prompt index (cap at 50, priority 7+ if over)
+       const index = this.buildPromptIndex();
+       
+       instructions += `\n\n${gateInstructions.replace('{{prompt_index}}', index)}`;
+     }
+     
+     return {
+       protocolVersion: '2024-11-05',
+       capabilities: { ... },
+       serverInfo: { ... },
+       instructions,
+     };
+   }
+   ```
+
+2. Build prompt index with cap:
+   - If <= 50 prompts: include all
+   - If > 50 prompts: include only priority 7+
+   - Format: `- <name>: <summary>` (~100 chars per entry)
+
+**Test Strategy:**
+
+- Unit test: Gated project includes gate instructions in initialize
+- Unit test: Prompt index included in instructions
+- Unit test: Index capped at 50 entries
+- Unit test: Over 50 prompts shows priority 7+ only
+- Unit test: Non-gated project skips gate instructions
+- Unit test: {{prompt_index}} template replaced
+- Integration test: End-to-end initialize with gated project