feat: fix registration 500, add forgot-password flow, frontend validation

- Fix MissingGreenlet: sync_engine now uses psycopg2 instead of asyncpg
- Fix bcrypt/passlib compat: pin bcrypt<4.1 in requirements
- Fix legacy password_hash NOT NULL: alter column to nullable in migration
- Add frontend password validation (uppercase + lowercase + digit)
- Add forgot-password and reset-password backend endpoints
- Add forgot-password and reset-password frontend pages
- Add email_service.py (SMTP via admin settings)
- Add reset_token/reset_token_expires columns to User model
- Migrate legacy JSON-only users to DB on password reset request
- Mount data/ volume in docker-compose.local.yml for persistence
- Add production deployment config (Dockerfile, nginx, deploy.sh)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker/backend/Dockerfile

@@ -1,7 +1,7 @@
 # Document Translation API - Backend Dockerfile
 # Multi-stage build for optimized production image
 
-FROM python:3.11-slim as builder
+FROM python:3.12-slim AS builder
 
 WORKDIR /app
 
@@ -22,7 +22,7 @@ RUN pip install --no-cache-dir --upgrade pip && \
     pip install --no-cache-dir -r requirements.txt
 
 # Production stage
-FROM python:3.11-slim as production
+FROM python:3.12-slim AS production
 
 WORKDIR /app