Feat: wall room creation and snap, stairs system

[sudhir9297]

What does this PR do?

This PR delivers a comprehensive upgrade to the editor by improving wall, room, slab, ceiling, and stair workflows, with a strong focus on curved wall support, automatic geometry updates, and more intuitive editing interactions.

It introduces:

• Full curved wall creation, editing, measurement, and geometry handling
• Smarter room, slab, and ceiling generation that adapts to both straight and curved walls
• Advanced wall editing UX including endpoint controls, detach behavior, and improved snapping
• Robust stair system integration with automatic slab and ceiling cutouts
• Improved handling of doors/windows during wall merges and edits
• Enhanced ceiling interaction, visibility, and selection directly in 3D
• A configurable grid snapping system for more precise control
• Multiple fixes for rendering, geometry stability, and interaction loops

All improvements are implemented within the existing architecture without introducing new global state or breaking existing workflows.

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Walls & Rooms

• Fixed auto room/slab recalculation when curved walls move by including curveOffset in wall change detection and using sampled curved edges.
• Improved slab handling around curved walls to prevent sharp spikes and align behavior with the existing room/slab generation flow.
• Reduced auto slab polygon density so curved-room slabs don’t expose excessive edit points.
• Moved shared polygon simplification logic into a reusable geometry utility.
• Added wall merge-on-divider-delete behavior so split walls recombine into a single wall.
• Improved merged-wall selection so walls with openings (doors/windows) are preserved as the surviving wall.
• Ensured slabs correctly adjust their cutouts when curved walls are modified.

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Wall Editing UX

• Added floating wall-end controls in both 2D (floorplan) and 3D for direct endpoint manipulation.
• Made connected walls follow endpoint movement in both preview and final state.
• Added Alt + drag behavior to temporarily detach connected walls while moving endpoints.
• Improved detach hint UI so it appears only in the correct context and state.
• Increased usability of wall corner controls and improved interaction priority.
• Enabled snapping-aware wall dragging for both straight and curved walls.
• Made endpoint angle snapping follow the active grid snap setting.
• Fixed curved wall drag infinite update loop by avoiding redundant preview updates.
• Allowed moving walls from a single corner with proper linkage handling.

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Wall Duplication

• Fixed 3D duplicate action so walls correctly duplicate instead of failing silently.
• Fixed duplicate vs move flow by creating the wall before entering move mode.
• Ensured duplicated walls remain unlinked during placement and link correctly afterward.

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Doors & Windows Behavior

• Prevented doors and windows from being placed on curved walls.
• Ensured wall openings (doors/windows) correctly reattach to the appropriate wall after divider deletion.
• When split walls are merged:
  • Openings return to the merged wall correctly.
  • Walls merge only if material/color matches; otherwise they remain separate.

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Ceilings

• Added automatic ceiling generation similar to slabs:
  • Auto-create from closed rooms
  • Auto-update on wall movement
  • Support curved wall reshaping
  • Auto split/merge with divider changes
• Updated naming convention to Room N Slab and Room N Ceiling.
• Fixed ceiling selection affordances to appear reliably on load.
• Introduced hot corner selection so ceilings can be selected directly without interfering with walls/floors.
• Improved ceiling affordance visuals:
  • Cleaner corner brackets
  • Reduced to 4 key handles
  • Smaller, more precise interaction targets
• Switched to rectangular hit areas for more predictable selection.
• Ensured ceiling selection resets stale interaction states before activating.
• Stabilized affordance system to avoid React update loops and render issues.
• Improved ceiling move interaction:
  • Added translucent drag preview (ghost ceiling)
  • Added clear boundary outline during movement for better visibility

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Stairs, Slabs & Ceiling Cutouts

• Added stair opening data:
  • fromLevelId
  • toLevelId
  • slabOpeningMode
  • openingOffset
• Added holeMetadata support for both slabs and ceilings.
• Built automatic synchronization between stairs and slab/ceiling cutouts.
• Wired cutout sync into the stair system for initial load and live updates.
• Added stair panel controls for:
  • From/To level selection
  • Opening configuration
• Updated stair tool defaults for improved initial behavior.
• Fixed stair placement so adding stairs on a specific floor keeps them on that floor.

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Hole Behavior & UI

• Updated slab, ceiling, and manual hole UI to correctly preserve:
  • Manually created holes
  • Stair-generated holes
• Ensured both types coexist without conflicts.

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Stair Cutout Geometry

• Implemented straight stair cutouts.
• Implemented landing cutouts and merged them with connected flight cutouts.
• Added support for larger straight-flight cutouts.
• Limited flight cutouts to only affect the top side of the flight.
• Added ceiling cutouts alongside slab cutouts for full vertical consistency.
• Added spiral stair circular cutout support.

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Snapping System

• Added a top-bar grid snap control in the editor toolbar.
• Persisted snap settings in editor state.
• Connected snapping logic across placement and wall drafting systems.
• Updated snap options:
  • Added: 0.25, 0.10, 0.05
  • Removed: 0.15
• Converted snap control from toggle button to dropdown.
• Reordered control placement for better UX.
• Standardized display format (e.g., 0.50 instead of 0.5).
• Kept grid visuals unchanged; only snapping behavior updated.

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Geometry & Rendering Stability

• Fixed curved wall measurement system:
  • Use curve length instead of straight chord
  • Measurement follows curve visually
  • Correct edge-to-edge measurement from wall face
  • Fixed endpoint anchoring
• Restored correct measurement behavior for straight walls.
• Ported curved wall mitering and junction logic from plan3D:
  • Improved intersection math using tangents
  • Refined wall footprint generation
  • Prevented sharp geometry artifacts at curved joins
• Fixed slab and ceiling geometry to always generate uv2, resolving material issues.
• Fixed WebGPU pipeline errors when modifying slab height with materials.
• Fixed render crashes related to sunken slabs.
• Fixed ceiling visibility during movement by adding outline feedback.

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Architecture Notes

• All changes remain within the existing architecture:
  • Same useEditor / useScene state system
  • Same node schemas
  • Same feature-based tool structure
• No new global state or alternate rendering pipeline introduced.