feat(animation): decompose AnimationController into FSM-based architecture

Replace the 2,200-line monolithic AnimationController (goto-driven,
single class, untestable) with a composed FSM architecture per
refactor.md.

New subsystem (src/rendering/animation/ — 16 headers, 10 sources):
- CharacterAnimator: FSM composer implementing ICharacterAnimator
- LocomotionFSM: idle/walk/run/sprint/jump/swim/strafe
- CombatFSM: melee/ranged/spell cast/stun/hit reaction/charge
- ActivityFSM: emote/loot/sit-down/sitting/sit-up
- MountFSM: idle/run/flight/taxi/fidget/rear-up (per-instance RNG)
- AnimCapabilitySet + AnimCapabilityProbe: probe once at model load,
  eliminate per-frame hasAnimation() linear search
- AnimationManager: registry of CharacterAnimator by GUID
- EmoteRegistry: DBC-backed emote command → animId singleton
- FootstepDriver, SfxStateDriver: extracted from AnimationController

animation_ids.hpp/.cpp moved to animation/ subdirectory (452 named
constants); all include paths updated.

AnimationController retained as thin adapter (~400 LOC): collects
FrameInput, delegates to CharacterAnimator, applies AnimOutput.

Priority order: Mount > Stun > HitReaction > Spell > Charge >
Melee/Ranged > CombatIdle > Emote > Loot > Sit > Locomotion.
STAY_IN_STATE policy when all FSMs return valid=false.

Bugs fixed:
- Remove static mt19937 in mount fidget (shared state across all
  mounted units) — replaced with per-instance seeded RNG
- Remove goto from mounted animation branch (skipped init)
- Remove per-frame hasAnimation() calls (now one probe at load)
- Fix VK_INDEX_TYPE_UINT16 → UINT32 in shadow pass

Tests (4 new suites, all ASAN+UBSan clean):
- test_locomotion_fsm: 167 assertions
- test_combat_fsm: 125 cases
- test_activity_fsm: 112 cases
- test_anim_capability: 56 cases

docs/ANIMATION_SYSTEM.md added (architecture reference).

src/game/game_handler.cpp

@@ -31,7 +31,7 @@
 #include "pipeline/asset_manager.hpp"
 #include "pipeline/dbc_loader.hpp"
 #include "core/logger.hpp"
-#include "rendering/animation_ids.hpp"
+#include "rendering/animation/animation_ids.hpp"
 #include <glm/gtx/quaternion.hpp>
 #include <algorithm>
 #include <cmath>
@@ -5145,7 +5145,7 @@ const std::vector<std::string>& GameHandler::getJoinedChannels() const {
 }
 
 // ============================================================
-// Phase 1: Name Queries (delegated to EntityController)
+// Name Queries (delegated to EntityController)
 // ============================================================
 
 void GameHandler::queryPlayerName(uint64_t guid) {
@@ -5217,7 +5217,7 @@ void GameHandler::emitAllOtherPlayerEquipment() {
 }
 
 // ============================================================
-// Phase 2: Combat (delegated to CombatHandler)
+// Combat (delegated to CombatHandler)
 // ============================================================
 
 void GameHandler::startAutoAttack(uint64_t targetGuid) {
@@ -5372,7 +5372,7 @@ void GameHandler::requestPvpLog() {
 }
 
 // ============================================================
-// Phase 3: Spells
+// Spells
 // ============================================================
 
 void GameHandler::castSpell(uint32_t spellId, uint64_t targetGuid) {
@@ -5489,7 +5489,7 @@ void GameHandler::sendAlterAppearance(uint32_t hairStyle, uint32_t hairColor, ui
 }
 
 // ============================================================
-// Phase 4: Group/Party
+// Group/Party
 // ============================================================
 
 void GameHandler::inviteToGroup(const std::string& playerName) {
@@ -5606,7 +5606,7 @@ void GameHandler::turnInPetition(uint64_t petitionGuid) {
 }
 
 // ============================================================
-// Phase 5: Loot, Gossip, Vendor
+// Loot, Gossip, Vendor
 // ============================================================
 
 void GameHandler::lootTarget(uint64_t guid) {