Add Fit to Frame and Upscale (print tools)

Backend — new /api/print/* router:
- POST /api/print/frame-fit: fit image to 4x6/5x7/8x10/11x14/16x20/20x24/24x36
  and square sizes (4x4/8x8/12x12) at configurable DPI.
  Three modes:
    crop   — center-crop to aspect ratio, Lanczos scale to print res (no AI)
    extend — scale to fill one dimension, AI-inpaint the gap; mirror-fill fallback
    smart  — auto: extend if gap < 15% of frame dimension, else crop
  Auto-detects orientation from image shape; respects explicit portrait/landscape.
- POST /api/print/upscale: Lanczos scale (always) or Real-ESRGAN (if installed)
- GET  /api/print/frame-sizes: frame catalogue with pixel dimensions at 300dpi
- GET  /api/print/upscale/available: reports whether Real-ESRGAN is installed

Frontend:
- modules/image/frame_fit.js: dialog with frame size, orientation, mode, DPI,
  optional extend prompt; shows current image size; result as new layer option
- modules/image/upscale.js: dialog with scale factor (1.5–4×), method selector
  (auto-hides AI option if Real-ESRGAN not available); result as new layer option
- config-menu.js: Fit to Frame... and Upscale... added under Image menu

https://claude.ai/code/session_01B58MaJCU1R6KwBDJCp8AfN

backend/app/main.py

@@ -8,7 +8,7 @@ import os
 
 from app.config import settings
 from app.database import init_db
-from app.routers import projects, edits, images, patches, generate, tools, ai_tools
+from app.routers import projects, edits, images, patches, generate, tools, ai_tools, print_tools
 
 
 @asynccontextmanager
@@ -42,6 +42,7 @@ app.include_router(patches.router)
 app.include_router(generate.router)
 app.include_router(tools.router)
 app.include_router(ai_tools.router)
+app.include_router(print_tools.router)
 
 
 @app.get("/api")