feat: add variation spawner and content repurposing

Variation spawner: select an image asset → spawn N variations that keep the
same emotional pattern/visual style but explore different hook angles. Runs
a focused ad-creative-designer agent with the original as a Gemini reference
image. New assets link back via parentAssetId.

Content repurposing: resize an image to all other platform dimensions using
Sharp (cover crop). Captions are re-toned for the target platform via Claude
CLI. No external APIs needed — fully local.

- Add parentAssetId self-relation to Asset model
- lib/repurpose.ts: Sharp resize, platform format mapping, caption re-toning
- lib/variations.ts: asset DNA extraction, variation prompt builder, mini-pipeline
- API routes: /api/assets/[id]/repurpose (GET formats, POST resize)
- API routes: /api/assets/[id]/variations (GET existing, POST spawn)
- Repurpose modal: checkbox list of target formats
- Variation modal: count picker, async launch
- Asset card: Repurpose + Variations buttons on image assets
- Asset lineage: "Derived from" shown on child assets

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/repurpose.ts

@@ -0,0 +1,95 @@
+import sharp from "sharp";
+import path from "path";
+import { mkdirSync } from "fs";
+import { runAgentStep } from "./claude";
+
+const PIPELINE_ROOT = process.env.PIPELINE_ROOT || path.join(process.cwd(), "pipeline");
+
+const PLATFORM_FORMATS: Record<string, { width: number; height: number; label: string }> = {
+  "instagram-feed": { width: 1080, height: 1080, label: "Instagram Feed" },
+  "instagram-stories": { width: 1080, height: 1920, label: "Instagram Stories" },
+  tiktok: { width: 1080, height: 1920, label: "TikTok" },
+  "nextdoor-spotlight": { width: 1200, height: 1200, label: "Nextdoor Spotlight" },
+  "nextdoor-display": { width: 1200, height: 628, label: "Nextdoor Display" },
+};
+
+export function getAvailableFormats(currentDimensions: string | null): string[] {
+  return Object.keys(PLATFORM_FORMATS).filter((key) => {
+    const fmt = PLATFORM_FORMATS[key];
+    return `${fmt.width}x${fmt.height}` !== currentDimensions;
+  });
+}
+
+export function getPlatformFormat(key: string) {
+  return PLATFORM_FORMATS[key] || null;
+}
+
+/**
+ * Resize an image to target platform dimensions using Sharp.
+ * Uses cover fit + center crop for aspect ratio changes.
+ */
+export async function resizeImage(
+  sourcePath: string,
+  targetFormat: string,
+  outputDir: string
+): Promise<{ filePath: string; fileName: string; dimensions: string; platform: string }> {
+  const fmt = PLATFORM_FORMATS[targetFormat];
+  if (!fmt) throw new Error(`Unknown format: ${targetFormat}`);
+
+  mkdirSync(path.join(PIPELINE_ROOT, outputDir), { recursive: true });
+
+  const sourceBase = path.basename(sourcePath, path.extname(sourcePath));
+  const fileName = `${sourceBase}_${targetFormat}_${fmt.width}x${fmt.height}.png`;
+  const outputPath = path.join(outputDir, fileName);
+  const fullOutputPath = path.join(PIPELINE_ROOT, outputPath);
+  const fullSourcePath = path.join(PIPELINE_ROOT, sourcePath);
+
+  await sharp(fullSourcePath)
+    .resize(fmt.width, fmt.height, { fit: "cover", position: "centre" })
+    .png()
+    .toFile(fullOutputPath);
+
+  const platform = targetFormat.split("-")[0];
+
+  return { filePath: outputPath, fileName, dimensions: `${fmt.width}x${fmt.height}`, platform };
+}
+
+/**
+ * Re-tone a caption for a different platform using Claude CLI.
+ */
+export async function retoneCaption(
+  originalCaption: string,
+  originalPlatform: string,
+  targetPlatform: string
+): Promise<string> {
+  const prompt = `You are a social media copywriter. Adapt this ${originalPlatform} caption for ${targetPlatform}.
+
+Original caption:
+${originalCaption}
+
+Rules:
+- ${targetPlatform === "tiktok" ? "Raw, authentic tone. Short. Trending hashtags. Hook in first line." : ""}
+- ${targetPlatform === "instagram" ? "Polished, aspirational. Hook → Value → CTA → Hashtags. 150-300 chars." : ""}
+- ${targetPlatform === "nextdoor" ? "Warm, neighborly. No hashtags. Reference local/community context." : ""}
+- Keep the core message but match the platform's voice.
+- Return ONLY the new caption text, nothing else.`;
+
+  const { output } = await runAgentStep("caption-retone", prompt, PIPELINE_ROOT, {});
+  return output.trim();
+}
+
+/**
+ * Repurpose an image asset to specific platform formats.
+ */
+export async function repurposeImage(
+  sourcePath: string,
+  targetFormats: string[],
+  outputDir: string
+): Promise<Array<{ filePath: string; fileName: string; dimensions: string; platform: string }>> {
+  const results = [];
+  for (const fmt of targetFormats) {
+    const result = await resizeImage(sourcePath, fmt, outputDir);
+    results.push(result);
+  }
+  return results;
+}