Fix critical bugs + add zoom/overlay for citizen chart

Bugs fixed:
- Auth middleware now works on page refresh (plugin restores
  auth from localStorage before middleware runs)
- Bezier drag no longer snaps back: removed client-side p0
  recalculation during drag, only server computes p0 on mouseUp
- Removed redundant /login.vue page (homepage already has links)

New features:
- Interactive zoom on Bezier chart (buttons + mouse wheel +
  tier 1/tier 2 presets)
- Toggle to display outlier vote curves (public overlay endpoint)
- Tier 1 curve visually emphasized (thicker stroke)
- Dev credentials file at data/DEV-CREDENTIALS.md

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

backend/app/routers/votes.py

@@ -39,6 +39,23 @@ async def _load_commune_context(commune_id: int, db: AsyncSession):
     return params, households
 
 
+# ── Public endpoint: overlay of all vote curves for citizens ──
+
+@router.get("/communes/{slug}/votes/current/overlay")
+async def current_overlay(slug: str, db: AsyncSession = Depends(get_db)):
+    """Public: returns all active vote curves (params only, no auth required)."""
+    commune = await _get_commune_by_slug(slug, db)
+    result = await db.execute(
+        select(Vote).where(Vote.commune_id == commune.id, Vote.is_active == True)
+    )
+    votes = result.scalars().all()
+    return [
+        {"vinf": v.vinf, "a": v.a, "b": v.b,
+         "c": v.c, "d": v.d, "e": v.e, "computed_p0": v.computed_p0}
+        for v in votes
+    ]
+
+
 # ── Public endpoint: current median curve for citizens ──
 
 @router.get("/communes/{slug}/votes/current")