Add interactive citizen page with sidebar, display settings, and adaptive CSS

Major rework of the citizen-facing page:
- Chart + sidebar layout (auth/vote/countdown in right sidebar)
- DisplaySettings component (font size, chart density, color palettes)
- Adaptive CSS with clamp() throughout, responsive breakpoints at 480/768/1024
- Baseline charts zoomed on first tier for small consumption detail
- Marginal price chart with dual Y-axes (foyers left, €/m³ right)
- Key metrics banner (5 columns: recettes, palier, prix palier, prix médian, mon prix)
- Client-side p0/impacts computation, draggable median price bar
- Household dots toggle, vote overlay curves
- Auth returns volume_m3, vote captures submitted_at
- Cleaned header nav (removed Accueil/Super Admin for public visitors)
- Terminology: foyer for bills, électeur for votes
- 600m³ added to impact reference volumes
- Realistic seed votes (50 votes, 3 profiles)

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

backend/app/models/models.py

@@ -48,9 +48,20 @@ class TariffParams(Base):
     recettes = Column(Float, default=75000.0)
     pmax = Column(Float, default=20.0)
     vmax = Column(Float, default=2100.0)
+    differentiated_tariff = Column(Boolean, default=False)
     data_year = Column(Integer, nullable=True)
     data_imported_at = Column(DateTime, nullable=True)
 
+    # Published Bézier curve (set by admin)
+    published_vinf = Column(Float, nullable=True)
+    published_a = Column(Float, nullable=True)
+    published_b = Column(Float, nullable=True)
+    published_c = Column(Float, nullable=True)
+    published_d = Column(Float, nullable=True)
+    published_e = Column(Float, nullable=True)
+    published_p0 = Column(Float, nullable=True)
+    published_at = Column(DateTime, nullable=True)
+
     commune = relationship("Commune", back_populates="tariff_params")