F14.1f — Add the guided-project setup and preview flow

[Flow-Fly]

Parent: #129. Final issue in the F14.1 foundation batch. Depends on the generator and guided-project creation service.

Scope

Add an accessible setup flow that previews the source and generated guide, exposes approachable presets, and creates a separate guided project.

Implementation

• Add pf-paint-by-number-dialog.ts using the existing dialog vocabulary.
• Select a local image and explain that processing stays on the device.
• Show source and generated guide previews together.
• Offer 16, 24, 32, and 48 long-side presets.
• Put advanced settings behind an explicit disclosure:
  • exact long-side size, including 64;
  • generated maximum color count;
  • generated or supplied restricted palette;
  • color or luminance mapping.
• Debounce preview generation and ignore stale async results.
• Use persistent labels, native form controls, visible focus, and a concise error/status region.
• Add a File menu entry. Project-browser placement remains in F14.3 — Finish guidance, resume, and entry points #131.

Acceptance

• Keyboard-only users can select a file, change presets/settings, inspect status, create, and cancel.
• Preview changes reflect current settings without stale-result flashes.
• Create is disabled until a valid guide exists.
• The dialog closes only after successful project creation.
• The current project remains intact on cancellation or errors.

Verification

• Component and stale-preview Vitest coverage
• npm run lint
• npm run test:run
• npm run build
• git diff --check

[Flow-Fly]

Completed in PR #310. The implementation is merged into develop at b3bf845 and the post-merge CI run 29084411483 passed.