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_096.md

@@ -0,0 +1,53 @@
+# Task ID: 96
+
+**Title:** Implement mcpctl delete stage Command
+
+**Status:** cancelled
+
+**Dependencies:** 79 ✓
+
+**Priority:** low
+
+**Description:** Add CLI command to delete a custom stage file (cannot delete built-ins).
+
+**Details:**
+
+Create `src/cli/src/commands/delete-stage.ts`:
+
+```typescript
+import { Command } from 'commander';
+import { unlink, access } from 'fs/promises';
+import { join } from 'path';
+import { listStages } from 'mcplocal/proxymodel/stage-registry';
+
+const STAGES_DIR = join(process.env.HOME ?? '', '.mcpctl', 'stages');
+
+export function registerDeleteStage(program: Command): void {
+  program
+    .command('delete stage <name>')
+    .description('Delete a custom stage')
+    .action(async (name: string) => {
+      const stages = listStages();
+      const stageInfo = stages.find(s => s.name === name);
+      
+      if (!stageInfo) {
+        console.error(`Stage '${name}' not found`);
+        process.exit(1);
+      }
+      
+      if (stageInfo.source === 'built-in') {
+        console.error(`Cannot delete built-in stage '${name}'`);
+        process.exit(1);
+      }
+      
+      const filePath = join(STAGES_DIR, `${name}.ts`);
+      await unlink(filePath);
+      
+      console.log(`Deleted ${filePath}`);
+    });
+}
+```
+
+**Test Strategy:**
+
+CLI test: can delete custom stage, cannot delete built-in stage (error message), deleting non-existent stage shows error.