fix: plugin no longer vanishes after Claude Code updates

Root cause: plugin registered as directory source in known_marketplaces.json,
which gets wiped on CLI updates. Now registers in extraKnownMarketplaces
(settings.json) as a GitHub source — same mechanism caveman/context-mode use.

Binaries install to ~/.claude-mnemonic/bin/ instead of the Claude-managed
plugins directory. Thin wrapper scripts in the repo let the marketplace
clone find them. Nothing gets cleaned up when Claude refreshes its cache.

Also fixed along the way:
- ONNX Runtime 1.24.3 → 1.26.0 (API v25 mismatch broke all embedding tests)
- Vector client leaked on DB reinit, processQueue had a race on sessionManager
- reloadConfig called os.Exit(0) bypassing graceful shutdown
- Removed dead QueryRowWithTimeout that leaked contexts
- Added tests for graph/watcher/maintenance/update (all were at 0%)

commands/restart.md

@@ -0,0 +1,21 @@
+# Restart Claude Mnemonic Worker
+
+Restart the claude-mnemonic worker process. Use this command when experiencing issues with the memory system.
+
+## Instructions
+
+1. Call the restart API endpoint using curl:
+   ```bash
+   curl -X POST http://127.0.0.1:37777/api/restart
+   ```
+
+2. Wait a moment for the worker to restart (typically 1-2 seconds)
+
+3. Verify the worker is running by checking the version:
+   ```bash
+   curl -s http://127.0.0.1:37777/api/version
+   ```
+
+4. Report the result to the user, including the version number from the response.
+
+If the restart fails, suggest the user check `/tmp/claude-mnemonic-worker.log` for errors.