add: track shared modules, vendor scripts, and update gitignore

- lib/common.py: shared run/load_json/save_json utilities
- webui/api/common.py: _ok/_error response helpers
- webui/static/htmx.min.js, json-enc.js: vendored frontend deps
- scripts/update-vendor.sh: frontend vendor updater
- vendor/acme.sh: bundled ACME client
- .gitignore: add .playwright-mcp/ and opencode.json.pwenv

.gitignore

@@ -14,6 +14,10 @@ __pycache__/
 
 # Local AI tool config (contains internal hostnames)
 opencode.json
+opencode.json.pwenv
+
+# Playwright MCP artifacts
+.playwright-mcp/
 
 # Runtime artifacts
 build/