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/routers/votes.py

@@ -103,29 +103,47 @@ async def current_curve(slug: str, db: AsyncSession = Depends(get_db)):
     )
     votes = result.scalars().all()
 
+    # Published curve from admin (if any)
+    published = None
+    if params.published_vinf is not None:
+        published = {
+            "vinf": params.published_vinf,
+            "a": params.published_a,
+            "b": params.published_b,
+            "c": params.published_c,
+            "d": params.published_d,
+            "e": params.published_e,
+            "p0": params.published_p0,
+        }
+
     if not votes:
-        # Return default Bézier curve (a=b=c=d=e=0.5, vinf=vmax/2)
-        default_vinf = params.vmax / 2
+        # Use published curve if available, otherwise default
+        if published:
+            dv, da, db_, dc, dd, de = published["vinf"], published["a"], published["b"], published["c"], published["d"], published["e"]
+        else:
+            dv, da, db_, dc, dd, de = 400, 0.5, 0.5, 0.5, 0.5, 0.5
+
         default_tariff = compute_tariff(
             households,
             recettes=params.recettes, abop=params.abop, abos=params.abos,
-            vinf=default_vinf, vmax=params.vmax, pmax=params.pmax,
-            a=0.5, b=0.5, c=0.5, d=0.5, e=0.5,
+            vinf=dv, vmax=params.vmax, pmax=params.pmax,
+            a=da, b=db_, c=dc, d=dd, e=de,
         )
         _, default_impacts = compute_impacts(
             households,
             recettes=params.recettes, abop=params.abop, abos=params.abos,
-            vinf=default_vinf, vmax=params.vmax, pmax=params.pmax,
-            a=0.5, b=0.5, c=0.5, d=0.5, e=0.5,
+            vinf=dv, vmax=params.vmax, pmax=params.pmax,
+            a=da, b=db_, c=dc, d=dd, e=de,
         )
 
         return {
             "has_votes": False,
             "vote_count": 0,
             "params": tariff_params,
+            "published": published,
             "median": {
-                "vinf": default_vinf, "a": 0.5, "b": 0.5,
-                "c": 0.5, "d": 0.5, "e": 0.5,
+                "vinf": dv, "a": da, "b": db_,
+                "c": dc, "d": dd, "e": de,
             },
             "p0": default_tariff.p0,
             "curve_volumes": default_tariff.curve_volumes,
@@ -166,6 +184,7 @@ async def current_curve(slug: str, db: AsyncSession = Depends(get_db)):
         "has_votes": True,
         "vote_count": len(votes),
         "params": tariff_params,
+        "published": published,
         "median": {
             "vinf": median.vinf,
             "a": median.a,