Add CodeMirror-based script editor, verified against real hardware

New Script section: loads the device's current Lua script (GET
/api/script), edits it in a real code editor (CodeMirror 6 with Lua
syntax highlighting via @codemirror/legacy-modes -- no dedicated
@codemirror/lang-lua package exists, verified against the npm
registry), and saves it back (POST /api/script) as raw text, not
JSON, matching the device's endpoint. Not Blockly yet -- that's its
own, much larger task; this is the raw-text step toward it.

Verified end-to-end against a real ESP32-C6: load, edit, save
hot-reloads on-device within one tick, and the change survives a
power cycle.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

package.json

@@ -8,6 +8,11 @@
     "build": "tsc && vite build",
     "preview": "vite preview"
   },
+  "dependencies": {
+    "@codemirror/language": "^6.0.0",
+    "@codemirror/legacy-modes": "^6.0.0",
+    "codemirror": "^6.0.0"
+  },
   "devDependencies": {
     "typescript": "^5.6.0",
     "vite": "^6.0.0"