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_101.md

@@ -0,0 +1,61 @@
+# Task ID: 101
+
+**Title:** Implement mcpctl cache clear Command
+
+**Status:** done
+
+**Dependencies:** 98 ✓
+
+**Priority:** low
+
+**Description:** Add CLI command to clear the proxymodel cache, optionally filtered by project.
+
+**Details:**
+
+Create `src/cli/src/commands/cache-clear.ts`:
+
+```typescript
+import { Command } from 'commander';
+import { readdir, unlink, rmdir } from 'fs/promises';
+import { join } from 'path';
+
+const CACHE_DIR = join(process.env.HOME ?? '', '.mcpctl', 'cache', 'proxymodel');
+
+export function registerCacheClear(program: Command): void {
+  program
+    .command('cache clear')
+    .description('Clear the proxymodel cache')
+    .option('--project <name>', 'Clear only cache for a specific project')
+    .option('--force', 'Skip confirmation', false)
+    .action(async (opts) => {
+      try {
+        const files = await readdir(CACHE_DIR);
+        const toDelete = opts.project 
+          ? files.filter(f => f.includes(opts.project))
+          : files;
+        
+        if (toDelete.length === 0) {
+          console.log('No cache entries to clear');
+          return;
+        }
+        
+        if (!opts.force) {
+          console.log(`This will delete ${toDelete.length} cache entries.`);
+          // Add confirmation prompt
+        }
+        
+        for (const file of toDelete) {
+          await unlink(join(CACHE_DIR, file));
+        }
+        
+        console.log(`Cleared ${toDelete.length} cache entries`);
+      } catch {
+        console.log('Cache directory does not exist');
+      }
+    });
+}
+```
+
+**Test Strategy:**
+
+CLI test: clears all entries without --project, clears filtered entries with --project, confirmation required without --force, --force skips confirmation.