Enhancement: Animate brightness for guarding and bloodied characters

## Summary
Add optional brightness animation effects for characters in two states:

- Guarding characters should subtly pulse between cyan brightness levels instead of remaining static.
- Bloodied characters should use a distinct dimming/pulsing cue that differentiates them from the guard tint.

## Rationale
- Improves moment-to-moment readability without relying on flashing effects.
- Preserves the cyan guard identity while making hurt state pop visually.
- Provides groundwork for future per-state visual polish.

## Requirements / Notes
- Must respect bank color constraints and per-TV standard palette limits.
- Ensure animation cadence does not reintroduce seizure risk (no hard flashing).
- Coordinate with LoadCharacterColors rewrite plans so both states share infrastructure.
- Guard tint remains cyan; animation should be brightness-only.
- Bloodied animation should play nicely with SECAM/B&W fallbacks.

## Dependencies
- GuardEffects.bas (guard tint application)
- Hurt-state color logic in LoadCharacterColors (pending rewrite)