Replace unique constraint with index on dailyCompletions

Changes unique constraint on (anonymousId, date) to a regular index for better performance and to support the migration logic where duplicates may temporarily exist before deduplication.

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

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

src/lib/server/db/schema.ts

@@ -39,7 +39,7 @@ export const dailyCompletions = sqliteTable('daily_completions', {
 	guessCount: integer('guess_count').notNull(),
 	completedAt: integer('completed_at', { mode: 'timestamp' }).notNull(),
 }, (table) => ({
-	uniqueCompletion: unique().on(table.anonymousId, table.date),
+	anonymousIdDateIndex: index('anonymous_id_date_idx').on(table.anonymousId, table.date),
 	dateIndex: index('date_idx').on(table.date),
 	dateGuessIndex: index('date_guess_idx').on(table.date, table.guessCount),
 }));