Enable TypeScript strict mode and fix all type errors

- Enable strict: true in tsconfig.json (was false)
- Add proper interfaces for all component props (Dashboard, Comparison, Slides)
- Add SlideConfig, ChartTypeOption, MetricOption types
- Type all function parameters, callbacks, and state variables
- Fix dynamic property access with proper keyof assertions
- 233 type errors resolved across 5 files

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

tsconfig.json

@@ -6,9 +6,7 @@
     "skipLibCheck": true,
     "esModuleInterop": true,
     "allowSyntheticDefaultImports": true,
-    "strict": false,
-    "noImplicitAny": false,
-    "strictNullChecks": false,
+    "strict": true,
     "forceConsistentCasingInFileNames": true,
     "noFallthroughCasesInSwitch": true,
     "module": "ESNext",