fix: createDefaultCombatState now uses discipline-aware channel stats

- Import computeChannelStats in combat-reset.ts
- Replace hardcoded channelSpeedMultiplier/channelDrainRate with computed values
- Fixes bug where resetCombat() lost discipline-modified channel stats
- Add regression tests in combat-reset-channel-stats.test.ts

docs/project-structure.txt

@@ -209,6 +209,7 @@ Mana-Loop/
 │   │   │   │   ├── bug-377-mana-auto-unlock.test.ts
 │   │   │   │   ├── bug-fixes.test.ts
 │   │   │   │   ├── combat-actions.test.ts
+│   │   │   │   ├── combat-reset-channel-stats.test.ts
 │   │   │   │   ├── combat-utils.test.ts
 │   │   │   │   ├── computed-stats.test.ts
 │   │   │   │   ├── conversion-pause-bug-regression.test.ts