[Feature] Pattern glow effects — purchasable add-on for territory patterns

## Overview
Each territory pattern can have a purchasable glow effect add-on. Sold separately ($4.99) or as a bundle with the pattern ($7.49). WebGL shader-driven. Each pattern has its own unique glow.

## Scope
- Glow effect system driven by pattern metadata
- Each pattern has a defined glow variant
- Glow purchasable as standalone add-on
- Bundle pricing: pattern + glow at discount vs buying separately
- Glow visible to all players in match

## Acceptance criteria
- [ ] Glow effects render correctly in WebGL
- [ ] Glow tied to pattern metadata system
- [ ] Standalone glow purchasable in shop ($4.99)
- [ ] Bundle (pattern + glow) available at $7.49
- [ ] Glow visible to all other players in match

## Dependencies
- **Depends on:** OAuth, pattern metadata system