feat(server): add study session API with FSRS integration

Implement study endpoints for spaced repetition learning:
- GET /api/decks/:deckId/study to fetch due cards
- POST /api/decks/:deckId/study/:cardId to submit reviews
- Integrate ts-fsrs library for scheduling algorithm
- Add ReviewLog repository for tracking review history

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

1 files changed, 62 insertions, 1 deletions

diff --git a/src/server/repositories/card.ts b/src/server/repositories/card.ts
index 0a47c50..76c9d30 100644
--- a/src/server/repositories/card.ts
+++ b/src/server/repositories/card.ts
@@ -1,4 +1,4 @@
-import { and, eq, isNull, sql } from "drizzle-orm";
+import { and, eq, isNull, lte, sql } from "drizzle-orm";
 import { db } from "../db/index.js";
 import { CardState, cards } from "../db/schema.js";
 import type { Card, CardRepository } from "./types.js";
@@ -99,4 +99,65 @@ export const cardRepository: CardRepository = {
 			.returning({ id: cards.id });
 		return result.length > 0;
 	},
+
+	async findDueCards(
+		deckId: string,
+		now: Date,
+		limit: number,
+	): Promise<Card[]> {
+		const result = await db
+			.select()
+			.from(cards)
+			.where(
+				and(
+					eq(cards.deckId, deckId),
+					isNull(cards.deletedAt),
+					lte(cards.due, now),
+				),
+			)
+			.orderBy(cards.due)
+			.limit(limit);
+		return result;
+	},
+
+	async updateFSRSFields(
+		id: string,
+		deckId: string,
+		data: {
+			state: number;
+			due: Date;
+			stability: number;
+			difficulty: number;
+			elapsedDays: number;
+			scheduledDays: number;
+			reps: number;
+			lapses: number;
+			lastReview: Date;
+		},
+	): Promise<Card | undefined> {
+		const result = await db
+			.update(cards)
+			.set({
+				state: data.state,
+				due: data.due,
+				stability: data.stability,
+				difficulty: data.difficulty,
+				elapsedDays: data.elapsedDays,
+				scheduledDays: data.scheduledDays,
+				reps: data.reps,
+				lapses: data.lapses,
+				lastReview: data.lastReview,
+				updatedAt: new Date(),
+				syncVersion: sql`${cards.syncVersion} + 1`,
+			})
+			.where(
+				and(
+					eq(cards.id, id),
+					eq(cards.deckId, deckId),
+					isNull(cards.deletedAt),
+				),
+			)
+			.returning();
+		return result[0];
+	},
 };