Feat(canvas): Add Lasso Tool with Freehand and Polygon modes

[DustyShoe]

Summary

• Added a new Lasso canvas tool with two modes: Freehand and Polygon.
• Added lasso tool button to the left toolbar (under Text) and mode switcher in the top options bar.
• Added lasso object type/state plumbing end-to-end:
  • new object state/type in canvas store
  • renderer support in object renderer/buffer renderer
  • addLasso API action + reducer path
• Implemented freehand behavior:
  • starts on primary pointer down
  • records contour continuously (including outside canvas bounds)
  • closes contour and commits on pointer up
• Implemented polygon behavior:
  • works on click (no Shift required to place points)
  • closes by clicking near the start point
  • start point is visible; hover over it enlarges indicator for close feedback
  • Shift enables angle snapping (45°) and start-point alignment behavior
• Preserved canvas UX rules:
  • middle click remains pan
  • right click remains context menu (not used by polygon lasso)
• Implemented Space-pan integration for active freehand session:
  • session is not canceled
  • contour remains visible while panning
  • cursor/canvas-relative behavior preserved when resuming drawing
• Subtract mode changed from Alt to modifier-based lasso compositing:
  • now uses Ctrl/Cmd (Meta) for destination-out (mac-safe)
• Added lasso availability guards:
  • disabled when there is no visible raster content
  • disabled when inpaint masks are globally hidden
  • if selected inpaint mask is disabled, commit goes to a newly created mask
• Fixed inpaint mask hidden-state edge cases:
  • reset hidden flag when mask collection becomes empty
  • corrected “all non-raster hidden” effective-state logic for empty categories
• Improved bbox correctness for erase/subtract shapes:
  • pixel-bbox path now accounts for pressure eraser and subtractive lasso objects
• Added hotkey L and related locale entries.
• Per agreement, no extra tooltip/hint UI was added in this PR.

QA Instructions

• Select lasso via toolbar and via L hotkey.
• Verify mode toggle (Freehand / Polygon) in top options bar.
• Freehand: draw and release -> contour closes and commits.
• Freehand: draw fast + outside canvas bounds -> stroke continues and commits.
• Freehand + Space: while pointer is still down, press/hold Space -> pan works immediately, contour stays visible, release Space -> continue drawing.
• Polygon: click to place points without Shift.
• Polygon: click start point to close contour.
• Polygon: start-point indicator is visible and enlarges on hover.
• Polygon + Shift: 45° snap works while placing segment.
• Middle click still pans canvas; right click still opens context menu.
• Subtract compositing works with Ctrl (Win/Linux) and Cmd (macOS).
• If no inpaint mask exists, first lasso commit creates a new inpaint mask.
• If selected mask is disabled, lasso commit creates/uses a new enabled mask.
• Lasso is blocked when all inpaint masks are globally hidden.
• Lasso is blocked when no visible raster layers with objects exist.
• Delete all mask layers after masks were hidden -> hidden state resets (tool no longer stuck disabled by stale flag).

Merge Plan

Simple merge.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• ❗Changes to a redux slice have a corresponding migration
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)