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>

ROADMAP.md

@@ -6,7 +6,7 @@
 ## Next
 - [x] **#1** Hide "next exercise" affordance until current exercise has ≥1 set
 - [x] Version display in Mini App footer — format `YYYY-MM-DD <short-sha>`. Primary path uses `git log`, pure-Python fallback parses `.git/HEAD` + loose commit objects for environments without git on PATH.
-- [ ] Semantic versioning tags — start tagging releases (`v0.1.0`, `v0.2.0`, ...) so the footer shows a human version instead of a SHA.
+- [x] ~~Semantic versioning tags — start tagging releases (`v0.1.0`, `v0.2.0`, ...) so the footer shows a human version instead of a SHA.~~ Decided against — keeping `YYYY-MM-DD <short-sha>` format.
 - [ ] **#7** Per-user workout numbering display (global ID stays as real key, just display transform)
 
 ## Soon