feat: multi-user SaaS, piani Freemium/Pro, Google OAuth, admin panel

BLOCCO 1 - Multi-user data model:
- User: email, display_name, avatar_url, auth_provider, google_id
- User: subscription_plan, subscription_expires_at, is_admin, post counters
- SubscriptionCode table per redeem codes
- user_id FK su Character, Post, AffiliateLink, EditorialPlan, SocialAccount, SystemSetting
- Migrazione SQLite-safe (ALTER TABLE) + preserva dati esistenti

BLOCCO 2 - Auth completo:
- Registrazione email/password + login multi-user
- Google OAuth 2.0 (httpx, no deps esterne)
- Callback flow: Google -> /auth/callback?token=JWT -> frontend
- Backward compat login admin con username

BLOCCO 3 - Piani e abbonamenti:
- Freemium: 1 character, 15 post/mese, FB+IG only, no auto-plans
- Pro: illimitato, tutte le piattaforme, tutte le feature
- Enforcement automatico in tutti i router
- Redeem codes con durate 1/3/6/12 mesi
- Admin panel: genera codici, lista utenti

BLOCCO 4 - Frontend completo:
- Login page design Leopost (split coral/cream, Google, social coming soon)
- AuthCallback per OAuth redirect
- PlanBanner, UpgradeModal con pricing
- AdminSettings per generazione codici
- CharacterForm con tab Account Social + guide setup

Deploy:
- Dockerfile con ARG VITE_BASE_PATH/VITE_API_BASE
- docker-compose.prod.yml per leopost.it (no subpath)
- docker-compose.yml aggiornato per lab

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

backend/app/models.py

@@ -1,6 +1,6 @@
 from datetime import datetime
 
-from sqlalchemy import Boolean, Column, DateTime, ForeignKey, Integer, JSON, String, Text
+from sqlalchemy import Boolean, Column, Date, DateTime, ForeignKey, Integer, JSON, String, Text
 
 from .database import Base
 
@@ -15,6 +15,30 @@ class User(Base):
     hashed_password = Column(String(255), nullable=False)
     created_at = Column(DateTime, default=datetime.utcnow)
 
+    # Multi-user SaaS fields
+    email = Column(String(255), unique=True, nullable=True)
+    display_name = Column(String(100), nullable=True)
+    avatar_url = Column(String(500), nullable=True)
+    auth_provider = Column(String(50), default="local")
+    google_id = Column(String(200), unique=True, nullable=True)
+    subscription_plan = Column(String(50), default="freemium")
+    subscription_expires_at = Column(DateTime, nullable=True)
+    is_admin = Column(Boolean, default=False)
+    posts_generated_this_month = Column(Integer, default=0)
+    posts_reset_date = Column(Date, nullable=True)
+
+
+class SubscriptionCode(Base):
+    __tablename__ = "subscription_codes"
+
+    id = Column(Integer, primary_key=True)
+    code = Column(String(100), unique=True, nullable=False)
+    duration_months = Column(Integer, nullable=False)  # 1, 3, 6, 12
+    created_by_admin_id = Column(Integer, ForeignKey("users.id"))
+    used_by_user_id = Column(Integer, ForeignKey("users.id"), nullable=True)
+    used_at = Column(DateTime, nullable=True)
+    created_at = Column(DateTime, default=datetime.utcnow)
+
 
 class Character(Base):
     __tablename__ = "characters"
@@ -31,6 +55,7 @@ class Character(Base):
     is_active = Column(Boolean, default=True)
     created_at = Column(DateTime, default=datetime.utcnow)
     updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=True)
 
 
 # === Phase 2: Content Generation ===
@@ -53,6 +78,7 @@ class Post(Base):
     status = Column(String(20), default="draft")  # draft, approved, scheduled, published, failed
     created_at = Column(DateTime, default=datetime.utcnow)
     updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=True)
 
 
 # === Phase 4: Affiliate Links ===
@@ -70,6 +96,7 @@ class AffiliateLink(Base):
     is_active = Column(Boolean, default=True)
     click_count = Column(Integer, default=0)
     created_at = Column(DateTime, default=datetime.utcnow)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=True)
 
 
 # === Phase 5: Scheduling ===
@@ -90,6 +117,7 @@ class EditorialPlan(Base):
     is_active = Column(Boolean, default=False)
     created_at = Column(DateTime, default=datetime.utcnow)
     updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=True)
 
 
 class ScheduledPost(Base):
@@ -124,6 +152,7 @@ class SocialAccount(Base):
     extra_data = Column(JSON, default=dict)  # platform-specific data
     is_active = Column(Boolean, default=True)
     created_at = Column(DateTime, default=datetime.utcnow)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=True)
 
 
 # === Phase 11: Comment Management ===
@@ -151,6 +180,7 @@ class SystemSetting(Base):
     __tablename__ = "system_settings"
 
     id = Column(Integer, primary_key=True, index=True)
-    key = Column(String(100), unique=True, nullable=False)
+    key = Column(String(100), nullable=False)
     value = Column(JSON)
     updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=True)