Image import wizard — shell + adjust step + 2 algorithms

[BernardJen]

Summary

First deliverable of the image import wizard (#4): the wizard shell, the image-adjust step, and 2 conversion algorithms. Ships a usable end-to-end import without waiting on the full algorithm library.

Scope

• Single "Upload image" entry replacing the separate PNG / SVG uploads.
• Wizard flow: upload → adjust → choose algorithm → tune → confirm.
• Adjust step: crop, scale/fit, rotate, brightness/contrast, threshold, invert.
• 2 algorithms with live preview + key parameters, e.g.:
  1. Edge detection / outline tracing
  2. Hatching by brightness
• Confirming adds the generated paths as objects into the scene (depends on Editing toolbar: select, copy/paste, and object manipulation #6 object model).

Acceptance criteria

• Single "Upload image" action replaces separate PNG/SVG uploads.
• Adjust step supports the basic edits above.
• 2 algorithms selectable, each with live preview + params.
• Confirm adds paths to the canvas as objects.

Notes

• Reuse src/plot/ (raster.ts, svg.ts, detail.ts).
• Additional algorithms tracked in Image import wizard — additional conversion algorithms (reach 5+) #12.
• Part of epic [Epic] Editor feature set: object model, pens, image import, projects #10.