MCP: add discrete typed tools (resize/crop/rotate/...)

[swperb]

Purpose: agents compose typed, named params far more reliably than a raw -vf DSL string. Strongest agent-UX win; ties into the MCP-registry discovery already set up.
Ease: 🟡 Mod — TypeScript additions in mcp/; the server assembles the filtergraph internally.

Tasks

• add tools: resize_image, crop_image, rotate_image, apply_color_filter, composite_images, convert_format
• typed params (width/height/filter_name/amount/...)
• keep convert_image as the power-user escape hatch
• bump mcp/ version + update mcp/README.md

[swperb]

Implementation notes

• File: mcp/src/index.ts. Follow the existing registerTool(name,{title,description,inputSchema},handler) + zod pattern (see convert_image). Each new tool builds a -vf string internally and calls the existing run([...]) helper (execFile, no shell — keep it that way).
• Mapping:
  • resize_image{input,output,width?,height?,keep_aspect?} → scale=W:H (use -1 for the unset axis)
  • crop_image{input,output,width,height,x?,y?} → crop=W:H:X:Y
  • rotate_image{input,output,degrees} → rotate=DEG (or transpose= for 90/180/270)
  • apply_color_filter{input,output,filter,amount?} → grayscale/sepia/brightness=V/contrast=V/…
  • composite_images{base,overlay,output,x?,y?} → second -i + overlay=X:Y
  • convert_format{input,output,quality?} → no -vf; just -q + extension
• Keep convert_image (raw -vf) as the power-user escape hatch.
• On release: bump version in mcp/package.json and mcp/server.json, then re-publish to npm + the MCP registry.