Fix NPC crashes with new SpellEffects and refactor healing & knockback logic

[Kamusvalenzuela]

Bugs fixed:

• Updated predicates (PredicateStunnedOrSleeping, PredicateUnableToCastSpells) to explicity return TRUE only for effects that actually block behavior
• All other effects safely return FALSE
  This removes unintended runtime crashes while preserving vanilla behavior

Healing modifier logic bug FIX

• Refactored Entity.ApplyHealingModifiers
• Healing boost and healing reduction now coexists
• Effects are grouped by category:
  • Multiple boosts = strongest boost only
  • Multiple reductions = strongest reduct only
• Final healing is calculated multiplicatively
  Formula:

FinalHeal = BaseHeal * (1 + MaxBoost) * (1 - MaxReduction)

This matches standar RPG behavior and prevents edge cases (e.g 100% reduction always blocks healing)

Knockback double-application & desync
Im still with troubles for fix this, and im searching new ways for solve this
Proyectile spells with knockback were aplying displacement:

• During projectile movement.
• Again on impact
  This caused:
• Server-side displacement stacking
• Client-side animation only showing the first knockback
• Resulting positional desync.
  FIX:
• I've tryed to apply knockback only once per hit, but seems to be not working fine
• Server and client positions remain in desync

Migration cleanup:

• Removed fragmented migration files helped by GeminiAI 3.0
• Consolidated them into a single migration:
  • 20251212000000_AddCombatEffects
• Applies to both SQLite and MySQL
  Added fields:
• Combat_KnockbackTiles (int)
• Combat_PercentageEffect (int?)

Verification

• Tested scenarios:
  • NPC Casting spells with new effects no longer crashed the server
  • Healing boost and healing reduction apply correctly and deterministically
  • Knockback tryes to behave consistently and visually matched with server position

NOTES:

• No database queries were added to combat calculations
• All logic operates on cached in-memory status data
• Vanilla behavior remains unchanged for existing SpellEffects