feat: spatial hash grid, off-screen double-buffering, virtual camera zoom/pan for GridMap

[Timrossid]

Scope

Rendering 500+ grid resource nodes with per-frame resource pulsation, status coloring, and connection lines causes significant UI lag on mid-range devices. This PR addresses the performance bottlenecks.

Changes

\src/utils/spatial.ts\ (new)

• SpatialHashGrid class — partitions the 2D canvas space into cells (\cellSize = NODE_RADIUS * 4 = 24px)
• Methods: \insert(node), \clear(), \query(bounds)\ — only returns nodes whose cells intersect the viewport
• Generic typed (\T extends { x: number; y: number }) for reusability

\src/components/spatial/GridMap.tsx\

• Off-screen canvas double-buffering — renders to an in-memory <canvas>\ buffer first, then copies to the visible canvas via \drawImage\ in a single composite step
• Spatial culling — only nodes intersecting the viewport (via SpatialHashGrid.query) are drawn each frame
• Virtual camera (\cameraRef) with zoom (scroll wheel, 0.5x–5x range) and pan (click-drag), transforms nodes via \ctx.translate/scale\
• devicePixelRatio-aware — canvas backing store sized as \clientWidth * dpr × clientHeight * dpr, context scaled by \dpr\ for sharp Retina output
• Debounced ResizeObserver (100ms) — prevents layout thrashing on resize
• Viewport-constrained grid lines — only grid lines intersecting the visible bounds are drawn
• Per-frame resource pulsation — sine-wave pulse (\sin(time * 0.002 + i)) applied each frame for the requested animated effect
• Pointer capture — \setPointerCapture\ for reliable drag tracking

Resolution Strategy

Requirement	Implementation
Spatial indexing	\SpatialHashGrid\ with \cellSize = 24, cells are keyed by \\:\\`
Off-screen double-buffer	\useRef\ created via \document.createElement('canvas'), composited with \drawImage\
Batch updates	All mutations collected in refs, flushed once per rAF frame via \
equestAnimationFrame\
DPR-aware	\window.devicePixelRatio\ read on each frame, canvas backing resized only when needed
Zoom/pan culling	Camera transform with \getViewportBounds\ → \SpatialHashGrid.query\ → only visible nodes drawn
Resize debounce	\ResizeObserver\ + \setTimeout(100ms)\ pattern

Closes #2

[elizabetheonoja-art]

fix errors so tests can pass