feat: Add nuke targeting halo visualization

[El-Magico777]

Description:

• Targeting cursor halo: Shows blast radius while selecting nuke targets

  • White semi-transparent circles (outer dotted, inner solid)
  • Follows cursor in world space, updates on mouse move
  • Supports both Atomic Bomb (30 tiles) and Hydrogen Bomb (100 tiles)
  • Auto-hides when targeting mode cancelled

• Flight-phase halo: Red indicator at impact point during nuke flight

  • Appears when nuke is launched, persists until detonation/interception
  • Uses same radius visualization as targeting cursor
  • Tracks multiple simultaneous nukes independently
  • Event-driven updates via GameUpdateType.Unit for performance

• Performance optimizations:

  • Event-driven active nuke tracking (Map<id, metadata>)
  • Resize-aware canvas redraw
  • Crisp pixel rendering (imageSmoothingEnabled = false)
  • Memory leak prevention (cleanup on unit removal)

• Architecture:

  • New NukeTargetingLayer with world-space transform support
  • Type-safe layer access via GameRenderer.getNukeTargetingLayer()
  • NukeImpactEvent emitted from FxLayer (currently unused after impact phase removal)
  • Integration with existing UIState.pendingBuildUnitType

Resolves nuke-target-halo user story requirements (AC1-AC6). Note: Post-impact fade phase was removed per user feedback; flight-phase halo only.

Please complete the following:

• I have added screenshots for all UI updates
• I process any text displayed to the user through translateText() and I've added it to the en.json file
• I have added relevant tests to the test directory
• I confirm I have thoroughly tested these changes and take full responsibility for any bugs introduced
• I understand that submitting code with bugs that could have been caught through manual testing blocks releases and new features for all contributors

Please put your Discord username so you can be contacted if a bug or regression is found:

el_magico777

[El-Magico777]

merged