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)
+);