fix: resolve mana conversion, Spire/Grimoire tab errors, and legacy store references

- Fix mana conversion to deduct from regen instead of mana pool (resolves player stuck at 1 mana below cap)
- Fix Spire Tab error by removing unused legacy import (store-modules/enemy-utils)
- Fix Grimoire Tab error by adding Array.isArray check for effects.map
- Move utility functions from legacy store-modules to utils/ to eliminate legacy dependencies
- Add regression test for mana conversion fix
- Update SpellsTab.tsx imports to use utils instead of legacy stores

docs/project-structure.txt

@@ -392,6 +392,7 @@ Mana-Loop/
 │       │   │   │   │   └── study-speed.test.ts
 │       │   │   │   ├── ui-store-tests/
 │       │   │   │   ├── equipment.test.ts
+│       │   │   │   ├── mana-conversion-fix.test.ts
 │       │   │   │   ├── mana.test.ts
 │       │   │   │   ├── regen.test.ts
 │       │   │   │   ├── skill.test.ts
@@ -426,11 +427,14 @@ Mana-Loop/
 │       │   │   ├── skills.ts
 │       │   │   └── spells.ts
 │       │   ├── utils/
+│       │   │   ├── activity-log.ts
 │       │   │   ├── combat-utils.ts
+│       │   │   ├── enemy-utils.ts
 │       │   │   ├── floor-utils.ts
 │       │   │   ├── formatting.ts
 │       │   │   ├── index.ts
-│       │   │   └── mana-utils.ts
+│       │   │   ├── mana-utils.ts
+│       │   │   └── room-utils.ts
 │       │   ├── computed-stats.ts
 │       │   ├── constants.ts
 │       │   ├── crafting-apply.ts