fix(practice): fix circular import causing REINFORCEMENT_CONFIG.creditMultipliers to be undefined

The issue was that progress-manager.ts was importing REINFORCEMENT_CONFIG
from @/db/schema/player-skill-mastery, which re-exported it from
@/lib/curriculum/config. This created a circular dependency that caused
the config object's creditMultipliers property to be undefined in production.

Root cause found via logging:
```
REINFORCEMENT_CONFIG.creditMultipliers=undefined, helpLevel=0
```

Fix:
- Import REINFORCEMENT_CONFIG directly from @/lib/curriculum/config/fluency-thresholds
- Remove unused re-export from player-skill-mastery.ts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/db/schema/player-skill-mastery.ts

@@ -1,12 +1,9 @@
 import { createId } from '@paralleldrive/cuid2'
 import { index, integer, sqliteTable, text, uniqueIndex } from 'drizzle-orm/sqlite-core'
 // Import tunable constants from centralized config
-import { FLUENCY_RECENCY, FLUENCY_THRESHOLDS, REINFORCEMENT_CONFIG } from '@/lib/curriculum/config'
+import { FLUENCY_RECENCY, FLUENCY_THRESHOLDS } from '@/lib/curriculum/config'
 import { players } from './players'
 
-// Re-export for backwards compatibility
-export { REINFORCEMENT_CONFIG }
-
 /**
  * Fluency state - computed from practice history, NOT stored in database
  * - practicing: isPracticing=true but hasn't achieved fluency criteria yet
@@ -144,7 +141,6 @@ export const FLUENCY_CONFIG = {
   ...FLUENCY_RECENCY,
 } as const
 
-// REINFORCEMENT_CONFIG imported from @/lib/curriculum/config and re-exported above
 
 /**
  * Check if a student has achieved fluency in a skill based on their practice history.

apps/web/src/lib/curriculum/progress-manager.ts

@@ -11,8 +11,9 @@ import {
   type FluencyState,
   type NewPlayerSkillMastery,
   type PlayerSkillMastery,
-  REINFORCEMENT_CONFIG,
 } from '@/db/schema/player-skill-mastery'
+// Import directly from source to avoid circular dependency issues with re-exports
+import { REINFORCEMENT_CONFIG } from '@/lib/curriculum/config/fluency-thresholds'
 import type { NewPracticeSession, PracticeSession } from '@/db/schema/practice-sessions'
 import type { HelpLevel } from '@/db/schema/session-plans'