feat: dynamic timeouts — scale with image size, respect PROCESSING_TIMEOUT_S

Create timeout.ts utility for dynamic timeout computation.
Replace hardcoded timeouts across the stack:
- tool-factory worker: 30s → dynamic based on megapixels
- Python bridge default: 300s → 600s (or env override)
- background-removal: fixed → dynamic based on image size
- OCR: fixed 600s → dynamic based on image size
- seam-carving: 120s → dynamic based on image size
- ExifTool: 30s → 60s
- HEIC converter: 30s → 120s
- SQLite busy_timeout: 5s → 10s

apps/api/src/routes/tool-factory.ts

@@ -15,6 +15,7 @@ import { sanitizeFilename } from "../lib/filename.js";
 import { decodeHeic } from "../lib/heic-converter.js";
 import type { WorkerInput, WorkerOutput } from "../lib/image-worker.js";
 import { sanitizeSvg } from "../lib/svg-sanitize.js";
+import { computeTimeout } from "../lib/timeout.js";
 import { getWorkerPool } from "../lib/worker-pool.js";
 import { createWorkspace } from "../lib/workspace.js";
 
@@ -227,8 +228,11 @@ export function createToolRoute<T>(app: FastifyInstance, config: ToolRouteConfig
               filename,
               inputFormat: validation.format,
             };
+            const meta = await sharp(fileBuffer).metadata();
+            const megapixels = ((meta.width ?? 0) * (meta.height ?? 0)) / 1_000_000;
+            const timeoutMs = computeTimeout(megapixels, "sharp");
             const workerResult: WorkerOutput = await pool.run(workerInput, {
-              signal: AbortSignal.timeout(30_000),
+              signal: AbortSignal.timeout(timeoutMs),
             });
             result = {
               buffer: Buffer.from(workerResult.buffer),