[switch87]

What does this PR change?

Implements #529: QR codes and barcodes as workpieces whose content is a template.

• Encoders.
  • Code 128 switches between code sets B and C on its own.
  • EAN-13 adds the check digit, or verifies it when 13 digits are given.
  • QR comes from segno (BSD-3, pure Python, no dependencies), with error correction L/M/Q/H.
• Dependency. segno==1.6.6 is added to requirements.txt, pixi.toml, pixi.lock, debian/control (python3-segno) and the Windows setup list. pixi.lock is regenerated with pixi lock.
• Barcode asset. A barcode asset implementing IGeometryProvider, so a barcode is an ordinary workpiece.
  • Modules are merged into closed outlines with holes, so both Engrave and Contour work.
  • Settings: module size, quiet zone, bar height, optional human-readable text, and invert for light codes on dark material.
• Templates. The content resolves {...} like a text box, so {counter} from feat: job counter variable for text templates #554 and {csv[...]} from feat: CSV merge for text templates #555 work once those land.
• UI and docs. Object → Add Barcode…, a Barcode properties group, and a docs page.
• Sketcher guard. A small is_sketch_workpiece() check, because the sketcher assumed every geometry provider is a sketch. This is a separate commit.

Why did you choose this specific architectural approach?

A barcode is a geometry provider asset, the same contract a sketch uses, so selection, transform, steps, the pipeline and save/load need no new code. Content goes through the existing template machinery, and the asset reports its template sources like a text box does. Outlines are built with raygeo (get_polygons_union, normalize_winding_orders) instead of Python polygon code. Settings change through the core UpdateAssetCommand, so undo works like for other assets. Lengths use LengthSpinRow, so they follow the user's unit. Everything lives in its own addon, so the core only gains the generic guard.

Open points:

• Template functions: {today()} and {uuid()} don't work in barcodes yet. Their registry lives in the sketcher addon, and addons can't import each other reliably; moving it into core would be a separate PR.
• Renderer: the barcode reuses the sketcher's renderer through the registry, hence requires: sketcher. A small generic fill renderer in core is an alternative.

How did you manually test this locally?

1. Object → Add Barcode…: a QR code "Rayforge" appears in the middle of the work area. Scan the screen with a phone: it reads "Rayforge".
2. In the Barcode properties, switch to Code 128 with content SN-{counter:05d} and human-readable text on: the text under the bars matches the counter. Change the length unit to inch: the size rows follow it.
3. Engrave and Contour both produce clean outlines in the preview, including the holes in QR modules. Invert gives a light code on dark material.
4. Undo of a settings change and save + reopen both keep the barcode.

Checklist

• I am not an AI. I have manually read the code and understand it.
• I take full responsibility for the quality and architectural fit of
  this code.
• I agree to publish this code under the MIT license.

[switch87]

I went through this PR again against the existing architecture and pushed a few corrections as separate commits (cc61601..1b4002f), so you can review just those:

• New barcodes are placed with MachinePanel.work_area_center() instead of my own math on machine.work_area, which was wrong for origins other than bottom-left.
• The contour orientation now uses raygeo's normalize_winding_orders() instead of a Python copy.
• Setting changes go through the existing UpdateAssetCommand, like the sketcher, instead of ChangePropertyCommand plus a custom descriptor and resize loop.
• Module size and bar height use LengthSpinRow, so they follow the user's length unit.
• The barcode icon moved into the addon's resources/icons, registered from its frontend like the other addons.
• is_sketch_workpiece is a TypeGuard now, so the asserts in the sketcher are gone.

The open points from the description still stand (renderer reuse from the sketcher, template functions, the hand-edited pixi.lock).