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

webui/api/common.py

@@ -0,0 +1,18 @@
+"""Shared API response helpers.
+
+Used by all API blueprints to produce consistent JSON responses
+per the API response contract: ``{"ok": true, "data": <value>}`` /
+``{"ok": false, "error": "msg"}``.
+"""
+
+from flask import jsonify
+
+
+def _ok(data=None):
+    """Return a success JSON response."""
+    return jsonify({"ok": True, "data": data})
+
+
+def _error(msg: str, code: int = 400):
+    """Return an error JSON response with the given HTTP status code."""
+    return jsonify({"ok": False, "error": msg}), code