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/static/json-enc.js

@@ -0,0 +1,12 @@
+htmx.defineExtension('json-enc', {
+  onEvent: function(name, evt) {
+    if (name === 'htmx:configRequest') {
+      evt.detail.headers['Content-Type'] = 'application/json'
+    }
+  },
+
+  encodeParameters: function(xhr, parameters, elt) {
+    xhr.overrideMimeType('text/json')
+    return (JSON.stringify(parameters))
+  }
+})