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/erase-object.ts

@@ -5,6 +5,7 @@ import { join, basename } from "node:path";
 import { inpaint } from "@stirling-image/ai";
 import { createWorkspace } from "../../lib/workspace.js";
 import { updateSingleFileProgress } from "../progress.js";
+import { validateImageBuffer } from "../../lib/file-validation.js";
 
 /**
  * Object eraser / inpainting route.
@@ -54,6 +55,15 @@ export function registerEraseObject(app: FastifyInstance) {
           .send({ error: "No mask image provided. Upload a mask as a second file with fieldname 'mask'" });
       }
 
+      const imageValidation = await validateImageBuffer(imageBuffer);
+      if (!imageValidation.valid) {
+        return reply.status(400).send({ error: `Invalid image: ${imageValidation.reason}` });
+      }
+      const maskValidation = await validateImageBuffer(maskBuffer);
+      if (!maskValidation.valid) {
+        return reply.status(400).send({ error: `Invalid mask: ${maskValidation.reason}` });
+      }
+
       try {
         const jobId = randomUUID();
         const workspacePath = await createWorkspace(jobId);