Migrate frontend from JavaScript to TypeScript

- Rename all 54 .js files to .ts, update esbuild entry point
- Add tsconfig.json, TypeScript devDependency, typecheck script
- Create types.ts with 25+ interfaces matching backend Pydantic schemas
  (Device, OutputTarget, ColorStripSource, PatternTemplate, ValueSource,
  AudioSource, PictureSource, ScenePreset, SyncClock, Automation, etc.)
- Make DataCache generic (DataCache<T>) with typed state instances
- Type all state variables in state.ts with proper entity types
- Type all create*Card functions with proper entity interfaces
- Type all function parameters and return types across all 54 files
- Type core component constructors (CardSection, IconSelect, EntitySelect,
  FilterList, TagInput, TreeNav, Modal) with exported option interfaces
- Add comprehensive global.d.ts for window function declarations
- Type fetchWithAuth with FetchAuthOpts interface
- Remove all (window as any) casts in favor of global.d.ts declarations
- Zero tsc errors, esbuild bundle unchanged

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/esbuild.mjs

@@ -7,7 +7,7 @@ const watch = process.argv.includes('--watch');
 
 /** @type {esbuild.BuildOptions} */
 const jsOpts = {
-    entryPoints: [`${srcDir}/js/app.js`],
+    entryPoints: [`${srcDir}/js/app.ts`],
     bundle: true,
     format: 'iife',
     outfile: `${outDir}/app.bundle.js`,