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/api/profile.py

@@ -19,6 +19,7 @@ class ProfileUpdate(BaseModel):
     resting_heart_rate: Optional[int] = None
     birth_year: Optional[int] = None
     height_cm: Optional[float] = None
+    biological_sex: Optional[str] = None
 
 
 class ProfileOut(BaseModel):
@@ -29,6 +30,7 @@ class ProfileOut(BaseModel):
     resting_heart_rate: Optional[int]
     birth_year: Optional[int]
     height_cm: Optional[float]
+    biological_sex: Optional[str]
     estimated_max_hr: Optional[int]
     is_admin: bool
 
@@ -72,6 +74,10 @@ async def update_profile(
         if not (50 <= body.height_cm <= 300):
             raise HTTPException(400, "Height must be 50–300 cm")
         current_user.height_cm = body.height_cm
+    if body.biological_sex is not None:
+        if body.biological_sex not in ('male', 'female', ''):
+            raise HTTPException(400, "biological_sex must be 'male' or 'female'")
+        current_user.biological_sex = body.biological_sex or None
 
     await db.commit()
     await db.refresh(current_user)