Health page: VO2 max gauge, layout improvements, 3Y/5Y trends, biological sex profile

- Add biological_sex field to User model, profile API, and ProfilePage toggle (male/female) — used to select the correct ACSM VO2 max threshold table
- Replace simple VO2 max number in daily snapshot with a colour-coded SVG radial gauge (Very Poor=red, Poor=orange, Fair=green, Good=blue, Excellent=purple) driven by sex- and age-appropriate thresholds
- Shrink Sleep widget to half-width, expand Heart & HRV to half-width; reorganise Heart & HRV internals into a 2×2 grid to reduce vertical height
- Add connectNulls + showDots to VO2 Max trend chart so sparse readings connect with a continuous line
- Add 3Y and 5Y range options to the Trends selector; increase allDays limit to 2000 for full 5yr snapshot navigation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -64,6 +64,15 @@ async def init_db():
     except Exception as e:
         print(f"health_metrics column migration skipped: {e}")
 
+    # biological_sex column on users added after initial creation
+    try:
+        async with engine.begin() as conn:
+            await conn.execute(text(
+                "ALTER TABLE users ADD COLUMN IF NOT EXISTS biological_sex VARCHAR(8)"
+            ))
+    except Exception as e:
+        print(f"users.biological_sex column migration skipped: {e}")
+
     # route_segments auto_generated column added after initial creation
     try:
         async with engine.begin() as conn: