feat(api): add generic tool route factory for all image tools

- createToolRoute<T> factory: handles multipart parsing, file validation,
  Zod settings validation, workspace management, and error handling
- Each tool only needs to provide toolId, settingsSchema, and process function
- Registers POST /api/v1/tools/:toolId routes automatically
- Tool registry stub at routes/tools/index.ts ready for tool implementations
- Catches Sharp errors and returns clean API error envelopes (422)

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

@@ -0,0 +1,15 @@
+import type { FastifyInstance } from "fastify";
+
+/**
+ * Registry that imports and registers all tool routes.
+ * Each tool uses the createToolRoute factory from tool-factory.ts.
+ *
+ * Tools will be added here as they are implemented in Phase 2 Tasks 4-10.
+ */
+export async function registerToolRoutes(app: FastifyInstance): Promise<void> {
+  // Tool routes will be registered here as they are implemented.
+  // Example:
+  //   const { registerResizeTool } = await import("./resize.js");
+  //   registerResizeTool(app);
+  app.log.info("Tool routes registered");
+}