feat: responsive canvas sizing and mobile touch support

[CristianEdwards]

Changes

• Responsive layout (<=1100px): Hide sidebar and inspector panels, canvas takes full viewport width with min-height: 50vh
• Phone breakpoint (<=640px): Reduced padding/gap, smaller border-radius, horizontally scrollable scenario/source/type picker bars
• touch-action: none: Prevents browser from intercepting canvas touch gestures (pan, pinch-to-page-zoom)
• Pinch-to-zoom: Tracks multiple active pointers; when two fingers are down, scales camera zoom proportionally to finger distance
• Pointer cleanup: Properly removes tracked pointers on pointerUp and pointerLeave and resets pinch state

Testing

• Build passes (tsc -b && vite build)
• All 18 unit tests pass
• Desktop layout unchanged at standard resolutions
• Mobile: canvas is now full-screen with working pinch-to-zoom