feat: add layout tools (collage, splitting, border/frame)

Add 3 layout and composition tools with API routes and frontend settings:
- collage: multi-image grid layout with configurable gap and background
- split: image grid splitting with ZIP output (reuses archiver pattern)
- border: borders, rounded corners via SVG mask, padding, and shadows

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

@@ -0,0 +1,111 @@
+import { z } from "zod";
+import sharp from "sharp";
+import archiver from "archiver";
+import type { FastifyInstance } from "fastify";
+import { randomUUID } from "node:crypto";
+import { basename, extname } from "node:path";
+
+const settingsSchema = z.object({
+  columns: z.number().min(1).max(10).default(2),
+  rows: z.number().min(1).max(10).default(2),
+});
+
+/**
+ * Split an image into grid parts and return as ZIP.
+ */
+export function registerSplit(app: FastifyInstance) {
+  app.post(
+    "/api/v1/tools/split",
+    async (request, reply) => {
+      let fileBuffer: Buffer | null = null;
+      let filename = "image";
+      let settingsRaw: string | null = null;
+
+      try {
+        const parts = request.parts();
+        for await (const part of parts) {
+          if (part.type === "file") {
+            const chunks: Buffer[] = [];
+            for await (const chunk of part.file) {
+              chunks.push(chunk);
+            }
+            fileBuffer = Buffer.concat(chunks);
+            filename = basename(part.filename ?? "image");
+          } else if (part.fieldname === "settings") {
+            settingsRaw = part.value as string;
+          }
+        }
+      } catch (err) {
+        return reply.status(400).send({
+          error: "Failed to parse multipart request",
+          details: err instanceof Error ? err.message : String(err),
+        });
+      }
+
+      if (!fileBuffer || fileBuffer.length === 0) {
+        return reply.status(400).send({ error: "No image file provided" });
+      }
+
+      let settings: z.infer<typeof settingsSchema>;
+      try {
+        const parsed = settingsRaw ? JSON.parse(settingsRaw) : {};
+        const result = settingsSchema.safeParse(parsed);
+        if (!result.success) {
+          return reply.status(400).send({ error: "Invalid settings", details: result.error.issues });
+        }
+        settings = result.data;
+      } catch {
+        return reply.status(400).send({ error: "Settings must be valid JSON" });
+      }
+
+      try {
+        const metadata = await sharp(fileBuffer).metadata();
+        const fullW = metadata.width ?? 0;
+        const fullH = metadata.height ?? 0;
+        const cellW = Math.floor(fullW / settings.columns);
+        const cellH = Math.floor(fullH / settings.rows);
+        const ext = extname(filename) || ".png";
+        const baseName = filename.replace(ext, "");
+
+        const jobId = randomUUID();
+
+        // Set up response headers for ZIP
+        reply.raw.writeHead(200, {
+          "Content-Type": "application/zip",
+          "Content-Disposition": `attachment; filename="split-${jobId.slice(0, 8)}.zip"`,
+          "Transfer-Encoding": "chunked",
+        });
+
+        const archive = archiver("zip", { zlib: { level: 5 } });
+        archive.pipe(reply.raw);
+
+        for (let row = 0; row < settings.rows; row++) {
+          for (let col = 0; col < settings.columns; col++) {
+            const left = col * cellW;
+            const top = row * cellH;
+            // Ensure we don't go out of bounds on the last row/col
+            const w = col === settings.columns - 1 ? fullW - left : cellW;
+            const h = row === settings.rows - 1 ? fullH - top : cellH;
+
+            const partBuffer = await sharp(fileBuffer)
+              .extract({ left, top, width: w, height: h })
+              .toBuffer();
+
+            archive.append(partBuffer, {
+              name: `${baseName}_r${row + 1}_c${col + 1}${ext}`,
+            });
+          }
+        }
+
+        await archive.finalize();
+      } catch (err) {
+        if (!reply.raw.headersSent) {
+          return reply.status(422).send({
+            error: "Split failed",
+            details: err instanceof Error ? err.message : "Unknown error",
+          });
+        }
+      }
+    },
+  );
+}