feat: per-user workout numbering (#7)

Display workouts as "#N" based on each user's own ordered list of
non-deleted workouts (rank by timestamp ascending). Global auto-
increment id stays the primary key, used only internally and in
exports. User-visible surfaces now all use the per-user number:
- /history listing
- /delete now accepts the per-user number
- Save confirmations (bot text and Mini App toast)

Deleting a workout renumbers the later ones downward, as expected
for a pure display transform.

New db helpers: get_user_workout_number, resolve_user_number, and
get_workouts now includes user_number per row via SQLite window
function.

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

webapp/app.js

@@ -580,7 +580,7 @@ btnSaveWorkout.addEventListener("click", async () => {
       showToast("Workout updated!");
     } else {
       data = await api("POST", "/workouts", { superset_groups, note });
-      showToast("Workout #" + data.workout_id + " saved!");
+      showToast("Workout #" + (data.user_number ?? data.workout_id) + " saved!");
     }
     workout = [];
     currentExercise = null;
@@ -610,7 +610,7 @@ document.getElementById("btn-save-raw").addEventListener("click", async () => {
     const data = await api("POST", "/workouts", { raw_text: raw });
     document.getElementById("inp-raw").value = "";
     clearDraft();
-    showToast("Workout #" + data.workout_id + " saved!");
+    showToast("Workout #" + (data.user_number ?? data.workout_id) + " saved!");
     tg.HapticFeedback.notificationOccurred("success");
   } catch (e) {
     showToast(e.message);