Background réaliste CsI(Tl) + hybridation mesuré/synthétique + dashboard continuum

- Remplace le continuum exponentiel par un modèle réaliste CsI(Tl) dans
  l'entraînement (bosse asymétrique ~110 keV + queue Compton)
- Ajoute l'injection de background mesuré (70% mesuré / 30% synthétique)
  via --measured_background et MEASURED_BACKGROUND_PATH
- Ajoute l'endpoint /api/background/continuum et le toggle "Continuum CsI"
  sur le dashboard background
- Exclut le canal 1023 (overflow bin) de l'affichage web (NUM_CHANNELS=1023)
- Corrige le lissage Gaussien du background (normalisation locale aux bords)
- Met à jour README.md, CLAUDE.md, TUTORIEL.md, TOTO.md, vega_ml/README.md

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

train/vega_ml/synthetic_spectra/generator.py

@@ -63,6 +63,7 @@ class SpectrumConfig:
     include_k40: bool = True
     include_radon: bool = True
     include_thorium: bool = True
+    measured_background_path: Optional[str] = None
     
     # Detector configuration
     detector_name: str = "radiacode_103"
@@ -166,7 +167,8 @@ class SpectrumGenerator:
                 include_k40=background_config.get('include_k40', True),
                 include_radon=background_config.get('include_radon', True),
                 include_thorium=background_config.get('include_thorium', True),
-                detector_config=self.detector_config
+                detector_config=self.detector_config,
+                measured_background_path=background_config.get('measured_background_path')
             )
             spectrum += bg_spectrum
             background_isotopes = bg_isotopes
@@ -264,6 +266,7 @@ class SpectrumGenerator:
                 'include_k40': config.include_k40,
                 'include_radon': config.include_radon,
                 'include_thorium': config.include_thorium,
+                'measured_background_path': config.measured_background_path,
             }
         )
         all_source_isotopes.extend(src_iso)