chore: remove dead code, add test infrastructure, update docs

- Delete 3 dead files: use-batch-processor.ts, use-i18n.ts, smart-crop.ts (AI package)
- Remove dead getJobProgress function and unused runPythonScript wrapper
- Remove 6 unused imports across API and web apps
- Remove unused shared types (ImageFormat, AppConfig, ApiError, HealthResponse, JobProgress)
  and constants (SUPPORTED_INPUT_FORMATS/OUTPUT_FORMATS, DEFAULT_OUTPUT_FORMAT)
- Remove unused store method (setOriginalBlobUrl) and clean AI package re-exports
- Add test infrastructure: vitest config, unit/integration/e2e tests, fixtures, screenshots
- Add Docker test infrastructure: Dockerfile.test, docker-compose.test.yml
- Add download_models.py for pre-baking AI model weights in Docker
- Add filename sanitization utility (apps/api/src/lib/filename.ts)
- Update .gitignore to exclude coverage/, *.tsbuildinfo, .superpowers/, test artifacts
- Update .dockerignore to exclude test/coverage/IDE artifacts from builds
- Update docs: remove smart crop from AI docs (uses Sharp directly), update bridge docs

packages/ai/src/bridge.ts

@@ -148,14 +148,3 @@ export function runPythonWithProgress(
   });
 }
 
-/**
- * Run a Python script from packages/ai/python/ with the given arguments.
- * Falls back to system python3 if the venv is not available.
- */
-export async function runPythonScript(
-  scriptName: string,
-  args: string[],
-  timeoutMs = 300000,
-): Promise<{ stdout: string; stderr: string }> {
-  return runPythonWithProgress(scriptName, args, { timeout: timeoutMs });
-}