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_031.md

@@ -0,0 +1,59 @@
+# Task ID: 31
+
+**Title:** Add DeepSeek API LLM provider
+
+**Status:** done
+
+**Dependencies:** 25 ✓
+
+**Priority:** medium
+
+**Description:** Implement DeepSeek API provider as a cheap cloud-based fallback when local LLMs are unavailable.
+
+**Details:**
+
+1. Create `src/mcplocal/src/providers/deepseek.ts`:
+   ```typescript
+   export class DeepSeekProvider implements LlmProvider {
+     readonly name = 'deepseek';
+     private apiKey: string;
+     private baseUrl = 'https://api.deepseek.com/v1';
+     
+     constructor(config: DeepSeekConfig) {
+       this.apiKey = config.apiKey || process.env.DEEPSEEK_API_KEY;
+     }
+     
+     async isAvailable(): Promise<boolean> {
+       return !!this.apiKey;
+     }
+     
+     async complete(options: CompletionOptions): Promise<CompletionResult> {
+       // DeepSeek uses OpenAI-compatible API
+       const response = await fetch(`${this.baseUrl}/chat/completions`, {
+         method: 'POST',
+         headers: {
+           'Authorization': `Bearer ${this.apiKey}`,
+           'Content-Type': 'application/json'
+         },
+         body: JSON.stringify({
+           model: 'deepseek-chat',
+           messages: [{ role: 'user', content: options.userPrompt }]
+         })
+       });
+       // Parse and return
+     }
+   }
+   ```
+2. Add DEEPSEEK_API_KEY to configuration
+3. Register in provider registry with medium priority
+4. Support both deepseek-chat and deepseek-coder models
+5. Add rate limiting handling
+
+**Test Strategy:**
+
+1. Unit test: Provider correctly checks API key availability
+2. Unit test: Request formatting matches DeepSeek API spec
+3. Unit test: Response parsing handles all fields
+4. Integration test: Full completion with actual API (with valid key)
+5. Test error handling for rate limits
+6. Test error handling for invalid API key