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>

.gitignore

@@ -48,3 +48,7 @@ backend/uploads/
 htmlcov/
 .coverage
 coverage.xml
+
+# Sensitive dev files
+IDENTIFIANTS.txt
+data/DEV-CREDENTIALS.md