Add guided drawing project foundation

[Flow-Fly]

Summary

• sample source images into deterministic pixel grids and generate bounded numbered guides
• support generated or restricted palettes, perceptual or luminance matching, and isolated-pixel simplification
• persist guided sessions inside project files and keep them isolated per workspace project
• add a File > New Guided Drawing flow with presets, advanced controls, local previews, and separate-project creation

Product contract

This is a creative scaffold for adult art users, not a strict correctness exercise. The generated target is durable guidance; the artist remains free to diverge. Number overlays, zoom-threshold behavior, painting guidance, and artist-controlled finishing remain in F14.2 and F14.3.

Issues

Closes #304
Closes #305
Closes #306
Closes #307
Closes #308
Closes #309

Part of #129 and #128.

Verification

• npm run test:run — 462 tests passed
• npm run lint -- --quiet
• npm run build
• npx fallow audit --changed-since origin/develop — no issues
• git diff --check

The production build retains the existing dynamic-import and large-chunk warnings.