feat: last-session recall when starting an exercise

When you start an exercise, the Mini App now fetches the most
recent time you logged it and shows a hint line in the sets card
("Last time: 8×60, 6×60, 5×60 · 3 days ago"), plus pre-fills the
weight input with the last set's weight.

- db.get_last_exercise(user_id, name): most recent non-deleted
  entry, case-insensitive name match, sets_detail parsed.
- GET /api/exercises/last?name=<name>.
- webapp: loadLastSession() on startExercise + draft restore;
  hint cleared on editExercise (the set rows are the reference
  there). Pre-fill only when the weight field is empty and no
  sets logged yet, so it never clobbers user input.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server.py

@@ -17,7 +17,7 @@ from urllib.parse import parse_qs
 
 from aiohttp import web
 
-from db import init_db, save_workout, get_workouts, get_workout_count, get_stats_sql, delete_workout, update_workout, export_workouts, get_user_workout_number, get_all_exercise_names, log_event, get_settings, update_settings
+from db import init_db, save_workout, get_workouts, get_workout_count, get_stats_sql, delete_workout, update_workout, export_workouts, get_user_workout_number, get_all_exercise_names, log_event, get_settings, update_settings, get_last_exercise
 from parser import parse_workout, format_workout
 
 logging.basicConfig(
@@ -283,6 +283,16 @@ async def api_get_exercise_names(request: web.Request):
     return web.json_response({"exercises": get_all_exercise_names()})
 
 
+@require_auth
+async def api_get_last_exercise(request: web.Request):
+    """Return the user's most recent logged entry for a given exercise name."""
+    name = request.query.get("name", "").strip()
+    if not name:
+        return web.json_response({"error": "Missing name"}, status=400)
+    last = get_last_exercise(request["user_id"], name)
+    return web.json_response({"last": last})
+
+
 @require_auth
 async def api_get_stats(request: web.Request):
     """Return summary stats for the user."""
@@ -366,6 +376,7 @@ def create_app() -> web.Application:
     app.router.add_put("/api/workouts/{workout_id}", api_update_workout)
     app.router.add_delete("/api/workouts/{workout_id}", api_delete_workout)
     app.router.add_get("/api/exercises", api_get_exercise_names)
+    app.router.add_get("/api/exercises/last", api_get_last_exercise)
     app.router.add_get("/api/stats", api_get_stats)
     app.router.add_get("/api/export/json", api_export_json)
     app.router.add_get("/api/export/csv", api_export_csv)