Export clean and dimensioned SVG plans from the TUI

[delaudio]

Goal

Allow Baumaus to generate a clean vector plan and a technical, dimensioned variant directly from the current document.

Scope

• Add a TUI command that exports plan.svg and plan-dimensions.svg.
• Keep plan.svg clean; include dimensions only in plan-dimensions.svg.
• Export walls, doors, and windows with consistent CAD coordinates: X to the right and Y upward.
• Use the derived-dimensions model from the preceding issue.
• Show export paths and errors in the status area.

Acceptance criteria

• Both SVGs open in browsers and vector-design tools.
• The dimensioned export includes main wall lengths plus opening dimensions and offsets.
• Labels remain legible.
• Tests cover the generated SVG output.