Feature: nutrition module (keto macros + intermittent fasting + electrolytes)

Backend:
- models/nutrition.py: NutritionGoal, Fast, ElectrolyteLog tables
- schemas/nutrition.py: Pydantic schemas for new endpoints
- routers/nutrition.py: /api/nutrition/{today,goals,fasts,electrolytes}
- main.py: register router + migration for new tables + seed keto point rules

Frontend:
- pages/Nutrition.jsx: macro bars, fast timer, eating window, electrolyte quick-add
- App.jsx: /nutrition route + Keto nav tab
- api.js: nutrition endpoints

Points schema for fasts (tier-based partial credit):
16:8=25, 18:6=40, 20:4=60, 24h=200, 36h=350, 48h=500, 72h=1000

Defaults tuned for Scot: 135kg M 44yo strict keto, 12:00-20:00 window,
Asia/Bangkok timezone, 2400/2600 cal rest/training, 20g net carb cap.

backend/app/schemas/nutrition.py

@@ -0,0 +1,67 @@
+from __future__ import annotations
+
+from datetime import datetime
+from pydantic import BaseModel
+
+
+class NutritionGoalIn(BaseModel):
+    calorie_target: int | None = None
+    protein_g_target: int | None = None
+    fat_g_target: int | None = None
+    net_carbs_g_cap: int | None = None
+    training_calorie_target: int | None = None
+    training_protein_g_target: int | None = None
+    training_fat_g_target: int | None = None
+    eating_window_start_hour: int | None = None
+    eating_window_end_hour: int | None = None
+    default_fast_hours: int | None = None
+    diet_style: str | None = None
+    timezone_str: str | None = None
+
+
+class NutritionGoalOut(BaseModel):
+    id: str
+    calorie_target: int
+    protein_g_target: int
+    fat_g_target: int
+    net_carbs_g_cap: int
+    training_calorie_target: int | None
+    training_protein_g_target: int | None
+    training_fat_g_target: int | None
+    eating_window_start_hour: int
+    eating_window_end_hour: int
+    default_fast_hours: int
+    diet_style: str
+    timezone_str: str
+
+
+class FastStart(BaseModel):
+    target_hours: int
+    fast_type: str = "daily"          # daily, weekly_24, long_48, long_72, extended
+    started_at: datetime | None = None  # defaults to now if omitted
+    notes: str | None = None
+
+
+class FastUpdate(BaseModel):
+    ended_at: datetime | None = None  # defaults to now if omitted, terminates the fast
+    notes: str | None = None
+
+
+class FastOut(BaseModel):
+    id: str
+    started_at: datetime
+    ended_at: datetime | None
+    target_hours: int
+    fast_type: str
+    completed: bool
+    broken_early: bool
+    points_awarded: int
+    elapsed_hours: float
+    notes: str | None
+
+
+class ElectrolyteIn(BaseModel):
+    sodium_mg: int = 0
+    potassium_mg: int = 0
+    magnesium_mg: int = 0
+    notes: str | None = None