fix: attunement system spec-vs-code discrepancies (issue #331)

- Fix conversion rate level scaling from linear (1+level*0.5) to exponential (1.5^(level-1)) in conversion-rates.ts
- Fix getAttunementLevelMultiplier formula to match spec §4.3
- Add level-up logging in attunementStore.ts via combat store addActivityLog
- Clarify getAttunementConversionRate returns flat base rate (level scaling applied separately)
- Update spec §8 to describe time-based puzzle room system matching code implementation
- Add 17 regression tests verifying exponential scaling, base rate behavior, and spec table values

docs/project-structure.txt

@@ -201,6 +201,7 @@ Mana-Loop/
 │   │   │   ├── __tests__/
 │   │   │   │   ├── achievements.test.ts
 │   │   │   │   ├── activity-log.test.ts
+│   │   │   │   ├── attunement-conversion-fix.test.ts
 │   │   │   │   ├── bug-fixes.test.ts
 │   │   │   │   ├── combat-actions.test.ts
 │   │   │   │   ├── combat-utils.test.ts