Initial commit

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/db/migrations/003_create_sessions.up.sql

@@ -0,0 +1,25 @@
+CREATE TABLE sessions (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    set_id     INTEGER NOT NULL REFERENCES training_sets(id),
+    started_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    ended_at   DATETIME,
+    note       TEXT DEFAULT ''
+);
+
+CREATE TABLE session_logs (
+    id            INTEGER PRIMARY KEY AUTOINCREMENT,
+    session_id    INTEGER NOT NULL REFERENCES sessions(id) ON DELETE CASCADE,
+    exercise_id   INTEGER NOT NULL REFERENCES exercises(id),
+    exercise_name TEXT NOT NULL,
+    set_number    INTEGER NOT NULL CHECK(set_number >= 1),
+    weight_kg     REAL NOT NULL CHECK(weight_kg >= 0 AND weight_kg <= 999),
+    reps          INTEGER NOT NULL CHECK(reps >= 0 AND reps <= 999),
+    note          TEXT DEFAULT '',
+    logged_at     DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    UNIQUE(session_id, exercise_id, set_number)
+);
+
+CREATE INDEX idx_sessions_set_id ON sessions(set_id);
+CREATE INDEX idx_sessions_started_at ON sessions(started_at);
+CREATE INDEX idx_session_logs_session_id ON session_logs(session_id);
+CREATE INDEX idx_session_logs_exercise_id ON session_logs(exercise_id);