chore(ai): add smoke test script (agent)

Added `scripts/agent/smoke-test.mjs` to verify key application flows in a headless environment.

Features:
- Verifies Relay Connection
- Verifies NSEC Login (Ephemeral)
- Verifies Video Publishing (Sign & Send)
- Verifies Event Retrieval
- Verifies DM Encryption/Decryption

Usage:
```bash
npm install
node scripts/agent/smoke-test.mjs
```

Artifacts (logs/reports) are generated in `artifacts/` and are ignored by git.
Utilizes `scripts/agent/simple-relay.mjs` for a local relay.
Uses `jsdom` to polyfill browser environment for `NostrClient`.

.gitignore

@@ -5,3 +5,4 @@ src/webtorrent-docs/
 playwright-report/
 test-results/
 tests/visual/__snapshots__/
+artifacts/