fix: add missing tsconfig files and restore npm run build

tsconfig.json, tsconfig.app.json, and tsconfig.node.json were never
committed because *.json was gitignored without exceptions for them.
Added whitelist entries and restored Dockerfile to use npm run build
(tsc -b + vite) now that the config files are present.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

flight-comparator/.gitignore

@@ -52,6 +52,9 @@ htmlcov/
 !tests/confirmed_flights.json
 !frontend/package.json
 !frontend/package-lock.json
+!frontend/tsconfig.json
+!frontend/tsconfig.app.json
+!frontend/tsconfig.node.json
 
 # Database files
 *.db