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

apps/api/src/routes/tools/compose.ts

@@ -5,6 +5,7 @@ import { randomUUID } from "node:crypto";
 import { writeFile } from "node:fs/promises";
 import { join } from "node:path";
 import { createWorkspace } from "../../lib/workspace.js";
+import { sanitizeFilename } from "../../lib/filename.js";
 
 const settingsSchema = z.object({
   x: z.number().min(0).default(0),
@@ -41,7 +42,7 @@ export function registerCompose(app: FastifyInstance) {
               overlayBuffer = buf;
             } else {
               baseBuffer = buf;
-              filename = part.filename ?? "image";
+              filename = sanitizeFilename(part.filename ?? "image");
             }
           } else if (part.fieldname === "settings") {
             settingsRaw = part.value as string;