fix: deactivate all disciplines when entering/exiting the Spire

- Add deactivateAll() action to discipline-slice.ts
- Call deactivateAll() in createEnterSpireMode() (combat-descent-actions.ts)
- Add spireMode guard in gameStore.ts tick() to skip discipline processTick
- Call deactivateAll() in exitSpireMode() (combatStore.ts) as safety measure
- Extract buildConversionParams to utils/conversion-params.ts to keep gameStore.ts under 400 lines
- Add regression tests (5 tests, all 1136 passing)

Fixes #347

docs/project-structure.txt

@@ -213,6 +213,7 @@ Mana-Loop/
 │   │   │   │   ├── cross-module-prestige-discipline.test.ts
 │   │   │   │   ├── curse-amplification.test.ts
 │   │   │   │   ├── design-validation-perk-gating.test.ts
+│   │   │   │   ├── discipline-deactivate-on-spire-entry.test.ts
 │   │   │   │   ├── discipline-math.test.ts
 │   │   │   │   ├── discipline-prerequisites.test.ts
 │   │   │   │   ├── discipline-reactivate-bug.test.ts
@@ -410,6 +411,7 @@ Mana-Loop/
 │   │   │   ├── utils/
 │   │   │   │   ├── activity-log.ts
 │   │   │   │   ├── combat-utils.ts
+│   │   │   │   ├── conversion-params.ts
 │   │   │   │   ├── conversion-rates.ts
 │   │   │   │   ├── discipline-math.ts
 │   │   │   │   ├── element-cap-bonus.ts