fix: add missing prefix to charts router

Charts router had no prefix, causing 404 errors.

Fixed:
- Added prefix="/api/charts" to APIRouter()
- Changed all endpoint paths from "/charts/..." to "/..."
  (prefix already includes /api/charts)

Now endpoints resolve correctly:
/api/charts/energy-balance
/api/charts/recovery-score
etc.

All 23 chart endpoints now accessible.

backend/routers/charts.py

@@ -62,13 +62,13 @@ from data_layer.correlations import (
 )
 from data_layer.utils import serialize_dates, safe_float, calculate_confidence
 
-router = APIRouter()
+router = APIRouter(prefix="/api/charts", tags=["charts"])
 
 
 # ── Body Charts ─────────────────────────────────────────────────────────────
 
 
-@router.get("/charts/weight-trend")
+@router.get("/weight-trend")
 def get_weight_trend_chart(
     days: int = Query(default=90, ge=7, le=365, description="Analysis window in days"),
     session: dict = Depends(require_auth)
@@ -185,7 +185,7 @@ def get_weight_trend_chart(
     }
 
 
-@router.get("/charts/body-composition")
+@router.get("/body-composition")
 def get_body_composition_chart(
     days: int = Query(default=90, ge=7, le=365),
     session: dict = Depends(require_auth)
@@ -249,7 +249,7 @@ def get_body_composition_chart(
     }
 
 
-@router.get("/charts/circumferences")
+@router.get("/circumferences")
 def get_circumferences_chart(
     max_age_days: int = Query(default=90, ge=7, le=365),
     session: dict = Depends(require_auth)
@@ -321,7 +321,7 @@ def get_circumferences_chart(
 # ── Nutrition Charts ────────────────────────────────────────────────────────
 
 
-@router.get("/charts/energy-balance")
+@router.get("/energy-balance")
 def get_energy_balance_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -419,7 +419,7 @@ def get_energy_balance_chart(
     }
 
 
-@router.get("/charts/macro-distribution")
+@router.get("/macro-distribution")
 def get_macro_distribution_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -509,7 +509,7 @@ def get_macro_distribution_chart(
     }
 
 
-@router.get("/charts/protein-adequacy")
+@router.get("/protein-adequacy")
 def get_protein_adequacy_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -623,7 +623,7 @@ def get_protein_adequacy_chart(
     }
 
 
-@router.get("/charts/nutrition-consistency")
+@router.get("/nutrition-consistency")
 def get_nutrition_consistency_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -707,7 +707,7 @@ def get_nutrition_consistency_chart(
 # ── Activity Charts ─────────────────────────────────────────────────────────
 
 
-@router.get("/charts/training-volume")
+@router.get("/training-volume")
 def get_training_volume_chart(
     weeks: int = Query(default=12, ge=4, le=52),
     session: dict = Depends(require_auth)
@@ -787,7 +787,7 @@ def get_training_volume_chart(
     }
 
 
-@router.get("/charts/training-type-distribution")
+@router.get("/training-type-distribution")
 def get_training_type_distribution_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -853,7 +853,7 @@ def get_training_type_distribution_chart(
     }
 
 
-@router.get("/charts/quality-sessions")
+@router.get("/quality-sessions")
 def get_quality_sessions_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -930,7 +930,7 @@ def get_quality_sessions_chart(
     }
 
 
-@router.get("/charts/load-monitoring")
+@router.get("/load-monitoring")
 def get_load_monitoring_chart(
     days: int = Query(default=28, ge=14, le=90),
     session: dict = Depends(require_auth)
@@ -1018,7 +1018,7 @@ def get_load_monitoring_chart(
     }
 
 
-@router.get("/charts/monotony-strain")
+@router.get("/monotony-strain")
 def get_monotony_strain_chart(
     days: int = Query(default=7, ge=7, le=28),
     session: dict = Depends(require_auth)
@@ -1078,7 +1078,7 @@ def get_monotony_strain_chart(
     }
 
 
-@router.get("/charts/ability-balance")
+@router.get("/ability-balance")
 def get_ability_balance_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -1152,7 +1152,7 @@ def get_ability_balance_chart(
     }
 
 
-@router.get("/charts/volume-by-ability")
+@router.get("/volume-by-ability")
 def get_volume_by_ability_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -1242,7 +1242,7 @@ def get_volume_by_ability_chart(
 # ── Recovery Charts ─────────────────────────────────────────────────────────
 
 
-@router.get("/charts/recovery-score")
+@router.get("/recovery-score")
 def get_recovery_score_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -1349,7 +1349,7 @@ def get_recovery_score_chart(
     }
 
 
-@router.get("/charts/hrv-rhr-baseline")
+@router.get("/hrv-rhr-baseline")
 def get_hrv_rhr_baseline_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -1451,7 +1451,7 @@ def get_hrv_rhr_baseline_chart(
     }
 
 
-@router.get("/charts/sleep-duration-quality")
+@router.get("/sleep-duration-quality")
 def get_sleep_duration_quality_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -1559,7 +1559,7 @@ def get_sleep_duration_quality_chart(
     }
 
 
-@router.get("/charts/sleep-debt")
+@router.get("/sleep-debt")
 def get_sleep_debt_chart(
     days: int = Query(default=28, ge=7, le=90),
     session: dict = Depends(require_auth)
@@ -1660,7 +1660,7 @@ def get_sleep_debt_chart(
     }
 
 
-@router.get("/charts/vital-signs-matrix")
+@router.get("/vital-signs-matrix")
 def get_vital_signs_matrix_chart(
     days: int = Query(default=7, ge=7, le=30),
     session: dict = Depends(require_auth)
@@ -1787,7 +1787,7 @@ def get_vital_signs_matrix_chart(
 # ── Correlation Charts ──────────────────────────────────────────────────────
 
 
-@router.get("/charts/weight-energy-correlation")
+@router.get("/weight-energy-correlation")
 def get_weight_energy_correlation_chart(
     max_lag: int = Query(default=14, ge=7, le=28),
     session: dict = Depends(require_auth)
@@ -1852,7 +1852,7 @@ def get_weight_energy_correlation_chart(
     }
 
 
-@router.get("/charts/lbm-protein-correlation")
+@router.get("/lbm-protein-correlation")
 def get_lbm_protein_correlation_chart(
     max_lag: int = Query(default=14, ge=7, le=28),
     session: dict = Depends(require_auth)
@@ -1915,7 +1915,7 @@ def get_lbm_protein_correlation_chart(
     }
 
 
-@router.get("/charts/load-vitals-correlation")
+@router.get("/load-vitals-correlation")
 def get_load_vitals_correlation_chart(
     max_lag: int = Query(default=14, ge=7, le=28),
     session: dict = Depends(require_auth)
@@ -1991,7 +1991,7 @@ def get_load_vitals_correlation_chart(
     }
 
 
-@router.get("/charts/recovery-performance")
+@router.get("/recovery-performance")
 def get_recovery_performance_chart(
     session: dict = Depends(require_auth)
 ) -> Dict:
@@ -2087,7 +2087,7 @@ def get_recovery_performance_chart(
 # ── Health Endpoint ──────────────────────────────────────────────────────────
 
 
-@router.get("/charts/health")
+@router.get("/health")
 def health_check() -> Dict:
     """
     Health check endpoint for charts API.