feat(webapp): show running version in Mini App footer

Compute `git describe --tags --always --dirty` at server startup
and expose via unauthenticated /api/version. Render as small muted
text at the bottom of the Mini App so the running version can be
confirmed at a glance.

Once tags exist, the badge will show e.g. v0.1.0 or v0.1.0-3-gSHA.
Until then it shows the short SHA.

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

server.py

@@ -9,6 +9,8 @@ import io
 import json
 import logging
 import os
+import pathlib
+import subprocess
 from urllib.parse import parse_qs
 
 from aiohttp import web
@@ -23,6 +25,24 @@ logging.basicConfig(
 logger = logging.getLogger(__name__)
 
 
+# ── Version (computed once at startup) ───────────────────────────
+
+def _compute_version() -> str:
+    """Return `git describe --tags --always --dirty`, or 'unknown'."""
+    try:
+        out = subprocess.run(
+            ["git", "describe", "--tags", "--always", "--dirty"],
+            cwd=pathlib.Path(__file__).parent,
+            capture_output=True, text=True, timeout=2, check=True,
+        )
+        return out.stdout.strip() or "unknown"
+    except (subprocess.SubprocessError, FileNotFoundError, OSError):
+        return "unknown"
+
+
+_VERSION = _compute_version()
+
+
 # ── Token (injected by start.py via env) ─────────────────────────
 
 def _get_bot_token() -> str:
@@ -206,6 +226,11 @@ async def api_export_json(request: web.Request):
     return web.json_response({"records": data, "count": len(data)})
 
 
+async def api_version(request: web.Request):
+    """Return the running server version. Unauthenticated."""
+    return web.json_response({"version": _VERSION})
+
+
 @require_auth
 async def api_export_csv(request: web.Request):
     """Export all workouts as CSV."""
@@ -239,9 +264,9 @@ def create_app() -> web.Application:
     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)
+    app.router.add_get("/api/version", api_version)
 
     # Serve the webapp/ folder
-    import pathlib
     webapp_dir = pathlib.Path(__file__).parent / "webapp"
 
     async def index_handler(request):