fix: AVIF sidecar crash, edit-metadata silent no-op, passport batch blank images, color-palette hex overflow, OCR log noise

- Convert all AI bridge inputs to PNG before writing to disk so PIL can
  read AVIF/WebP/TIFF (7 bridge files; face-detection and OCR already
  had this pattern)
- Add title/author aliases to edit-metadata schema so common field names
  actually write EXIF tags instead of being silently stripped by Zod
- Port extend/pad crop logic from passport-photo single endpoint to the
  batch pipeline so crop regions extending beyond the image get filled
  with background color instead of producing all-white output
- Clamp quantized color channels to 255 in color-palette to prevent
  Math.round(255/16)*16=256 from producing invalid hex like #100100100
- Compare OCR fallback warning against expected engine name per tier
  instead of comparing engine name against tier name (always mismatch)

packages/ai/src/background-removal.ts

@@ -20,7 +20,8 @@ export async function removeBackground(
   const inputPath = join(tmpdir(), `rembg_in_${id}.png`);
   const outputPath = join(outputDir, `rembg_out_${id}.png`);
 
-  await writeFile(inputPath, inputBuffer);
+  const pngBuffer = await sharp(inputBuffer).png().toBuffer();
+  await writeFile(inputPath, pngBuffer);
   try {
     const meta = await sharp(inputBuffer).metadata();
     const megapixels = ((meta.width ?? 0) * (meta.height ?? 0)) / 1_000_000;