feat: SQLite migrations and db pool with FK pragma

backend/migrations/001_initial.sql

@@ -0,0 +1,69 @@
+CREATE TABLE courses (
+    id       INTEGER PRIMARY KEY,
+    name     TEXT NOT NULL,
+    semester TEXT NOT NULL
+);
+
+CREATE TABLE tutors (
+    id            INTEGER PRIMARY KEY,
+    name          TEXT NOT NULL,
+    email         TEXT UNIQUE NOT NULL,
+    password_hash TEXT NOT NULL
+);
+
+CREATE TABLE tutor_courses (
+    tutor_id  INTEGER REFERENCES tutors(id),
+    course_id INTEGER REFERENCES courses(id),
+    PRIMARY KEY (tutor_id, course_id)
+);
+
+CREATE TABLE students (
+    id        INTEGER PRIMARY KEY,
+    course_id INTEGER NOT NULL REFERENCES courses(id),
+    name      TEXT NOT NULL
+);
+
+CREATE TABLE rooms (
+    id          INTEGER PRIMARY KEY,
+    name        TEXT NOT NULL,
+    layout_json TEXT NOT NULL
+);
+
+CREATE TABLE sessions (
+    id        INTEGER PRIMARY KEY,
+    course_id INTEGER NOT NULL REFERENCES courses(id),
+    week_nr   INTEGER NOT NULL,
+    date      TEXT NOT NULL CHECK (date GLOB '????-??-??'),
+    UNIQUE(course_id, week_nr)
+);
+
+CREATE TABLE slots (
+    id         INTEGER PRIMARY KEY,
+    session_id INTEGER NOT NULL REFERENCES sessions(id),
+    room_id    INTEGER REFERENCES rooms(id),
+    tutor_id   INTEGER NOT NULL REFERENCES tutors(id),
+    start_time TEXT NOT NULL,
+    end_time   TEXT NOT NULL,
+    status     TEXT NOT NULL DEFAULT 'closed',
+    code       TEXT UNIQUE
+);
+
+CREATE TABLE attendances (
+    id            INTEGER PRIMARY KEY,
+    slot_id       INTEGER NOT NULL REFERENCES slots(id),
+    student_id    INTEGER NOT NULL REFERENCES students(id),
+    seat_id       TEXT,
+    checked_in_at TEXT NOT NULL CHECK (checked_in_at GLOB '????-??-??T??:??:??*'),
+    UNIQUE(slot_id, student_id),
+    UNIQUE(slot_id, seat_id)
+);
+
+CREATE TABLE notes (
+    id         INTEGER PRIMARY KEY,
+    slot_id    INTEGER NOT NULL REFERENCES slots(id),
+    student_id INTEGER NOT NULL REFERENCES students(id),
+    tutor_id   INTEGER NOT NULL REFERENCES tutors(id),
+    content    TEXT NOT NULL DEFAULT '',
+    updated_at TEXT NOT NULL CHECK (updated_at GLOB '????-??-??T??:??:??*'),
+    UNIQUE(slot_id, student_id, tutor_id)
+);

backend/src/db.rs

@@ -1,5 +1,45 @@
-use sqlx::SqlitePool;
+use sqlx::{sqlite::SqlitePoolOptions, SqlitePool};
 
 pub async fn init() -> Result<SqlitePool, sqlx::Error> {
-    todo!()
+    let url = std::env::var("DATABASE_URL")
+        .unwrap_or_else(|_| "sqlite:attendance.db".into());
+    let pool = SqlitePoolOptions::new()
+        .after_connect(|conn, _| Box::pin(async move {
+            sqlx::query("PRAGMA foreign_keys = ON")
+                .execute(conn).await?;
+            Ok(())
+        }))
+        .connect(&url).await?;
+    sqlx::migrate!("./migrations").run(&pool).await?;
+    Ok(pool)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // NOTE: #[sqlx::test] injects its own pool, bypassing after_connect.
+    // We test FK enforcement behaviorally: insert a row with a bad FK and assert it fails.
+    // after_connect is manually invoked in the test setup below.
+    #[sqlx::test(migrations = "./migrations")]
+    async fn foreign_keys_enforced(pool: SqlitePool) {
+        // Enable FK for this test connection (mirrors what after_connect does in production)
+        sqlx::query("PRAGMA foreign_keys = ON").execute(&pool).await.unwrap();
+
+        let err = sqlx::query(
+            "INSERT INTO students (course_id, name) VALUES (999, 'Ghost')"
+        ).execute(&pool).await;
+        assert!(err.is_err(), "FK violation should be rejected when foreign_keys = ON");
+    }
+
+    #[sqlx::test(migrations = "./migrations")]
+    async fn all_tables_exist(pool: SqlitePool) {
+        for table in &["courses","tutors","tutor_courses","students","rooms",
+                       "sessions","slots","attendances","notes"] {
+            let count: (i64,) = sqlx::query_as(
+                "SELECT count(*) FROM sqlite_master WHERE type='table' AND name=?"
+            ).bind(table).fetch_one(&pool).await.unwrap();
+            assert_eq!(count.0, 1, "table {table} missing");
+        }
+    }
 }