design: WorkoutPage Hevy-style redesign + AlternativeModal + backend API

- Add GET /api/exercises/:id/alternatives endpoint
- Add GET /api/exercises/:id/last-workout endpoint
- New AlternativeModal component for swapping exercises
- WorkoutPage: single-tap logging, +/- buttons, rest timer
- Updated Icons with new workout icons
- Polish: card shadows, borders, micro-interactions
- Tasks directory for project management

backend/src/index.js

@@ -248,6 +248,61 @@ app.get('/api/days/:dayId/exercises', async (req, res) => {
   }
 });
 
+// Get alternative exercises for a given exercise (same muscle group)
+app.get('/api/exercises/:id/alternatives', async (req, res) => {
+  try {
+    const exerciseResult = await pool.query(
+      'SELECT muscle_group FROM exercises WHERE id = $1',
+      [req.params.id]
+    );
+
+    if (!exerciseResult.rows.length) {
+      return res.status(404).json({ error: 'Exercise not found' });
+    }
+
+    const muscleGroup = exerciseResult.rows[0].muscle_group;
+    const alternatives = await pool.query(
+      `SELECT id, name, muscle_group, description
+       FROM exercises
+       WHERE muscle_group = $1 AND id <> $2
+       ORDER BY name`,
+      [muscleGroup, req.params.id]
+    );
+
+    res.json(alternatives.rows);
+  } catch (err) {
+    console.error('Error fetching alternatives:', err);
+    res.status(500).json({ error: 'Database error' });
+  }
+});
+
+// Get last workout for a specific exercise id
+app.get('/api/exercises/:id/last-workout', async (req, res) => {
+  try {
+    const { user_id } = req.query;
+    const result = await pool.query(`
+      WITH latest AS (
+        SELECT wl.date
+        FROM workout_logs wl
+        JOIN program_exercises pe ON wl.program_exercise_id = pe.id
+        WHERE pe.exercise_id = $1 AND wl.user_id = $2
+        ORDER BY wl.date DESC
+        LIMIT 1
+      )
+      SELECT wl.*
+      FROM workout_logs wl
+      JOIN program_exercises pe ON wl.program_exercise_id = pe.id
+      JOIN latest l ON wl.date = l.date
+      WHERE pe.exercise_id = $1 AND wl.user_id = $2
+      ORDER BY wl.set_number ASC
+    `, [req.params.id, user_id || 1]);
+    res.json(result.rows);
+  } catch (err) {
+    console.error('Error fetching last workout for exercise:', err);
+    res.status(500).json({ error: 'Database error' });
+  }
+});
+
 // Get workout logs for a user and date
 app.get('/api/logs', async (req, res) => {
   try {