Add precision mode threshold system for know-your-world magnifier:
**Precision Mode Threshold System:**
- Constant PRECISION_MODE_THRESHOLD = 20 px/px
- Caps zoom when not in pointer lock to prevent exceeding threshold
- Shows clickable notice when threshold reached
- Activates pointer lock for precision control
**Pixel Grid Visualization:**
- Shows gold grid overlay aligned with crosshair
- Each grid cell = 1 screen pixel of mouse movement on main map
- Fades in from 70% to 100% of threshold (14-20 px/px)
- Fades out from 100% to 130% of threshold (20-26 px/px)
- Visible in both normal and precision modes
**Visual "Disabled" State:**
- Magnifier dims (60% brightness, 50% saturation) when at threshold
- Indicates zoom is capped until precision mode activated
- Returns to normal appearance in precision mode
**User Experience:**
- Below 14 px/px: Normal magnifier
- 14-20 px/px: Grid fades in as warning
- At 20 px/px: Full grid, dimmed magnifier, "Click here (not map) for precision mode"
- Click magnifier label (not map) to activate pointer lock
- In precision mode: Grid fades out (20-26 px/px), magnifier returns to normal
- e.stopPropagation() prevents accidental region clicks
**Debug Mode:**
- SHOW_MAGNIFIER_DEBUG_INFO flag (dev only)
- Shows technical info: zoom level and px/px ratio
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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