fix(migrations): merge main and rechain compliance migration as 031 after 030_add_mobile_devices

Merge main branch into compliance templates feature branch.

Main had advanced with migrations 027-030 (ensure_shared_links,
audit_logs, user_language_preference, mobile_devices) since this
branch forked. Our compliance migration was 027 with down_revision
026, which conflicted with main's 027_ensure_shared_links_table.

Changes:
- Merge main (including i18n, audit logs, mobile, GraphQL features)
- Resolve conflicts in app/api/__init__.py, app/models.py, tests/conftest.py
- Rename 027_add_compliance_templates → 031_add_compliance_templates
- Rechain: down_revision 026_add_scheduled_jobs → 030_add_mobile_devices
- Add ComplianceTemplate to migrations/env.py imports
- Alembic now has single head: 031_add_compliance_templates

app/models.py

@@ -146,6 +146,27 @@ class SettingsAuditLog(Base):
     action = Column(String, nullable=False)  # "update" or "delete"
 
 
+class AuditLog(Base):
+    """Comprehensive audit log for compliance tracking.
+
+    Records all significant actions: login/logout, document CRUD, settings
+    changes, and administrative operations.  Rows are append-only; the API
+    and service layer never update or delete entries.
+    """
+
+    __tablename__ = "audit_logs"
+
+    id = Column(Integer, primary_key=True, index=True)
+    timestamp = Column(DateTime(timezone=True), server_default=func.now(), nullable=False, index=True)
+    user = Column(String, nullable=False, index=True)  # Username or "anonymous" / "system"
+    action = Column(String, nullable=False, index=True)  # e.g. "login", "document.create", "settings.update"
+    resource_type = Column(String, nullable=True, index=True)  # e.g. "document", "user", "settings"
+    resource_id = Column(String, nullable=True)  # ID of the affected resource
+    ip_address = Column(String, nullable=True)  # Client IP address
+    details = Column(Text, nullable=True)  # JSON-encoded extra context
+    severity = Column(String(16), nullable=False, server_default="info")  # info / warning / error / critical
+
+
 class SavedSearch(Base):
     """User-defined saved search filters for quick access to frequently used filter combinations."""
 
@@ -256,6 +277,10 @@ class UserProfile(Base):
     preferred_destination = Column(String(50), nullable=True)
     stripe_customer_id = Column(String(64), nullable=True)
 
+    # UI language preference for i18n (ISO 639-1 code, e.g. "en", "de", "fr")
+    # NULL means "auto-detect from browser Accept-Language header"
+    preferred_language = Column(String(10), nullable=True)
+
     created_at = Column(DateTime(timezone=True), server_default=func.now())
     updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())
 
@@ -835,6 +860,40 @@ class ScheduledJob(Base):
     updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())
 
 
+class MobileDevice(Base):
+    """Registered mobile device for push notifications.
+
+    Stores the push token (Expo push token, FCM token, or APNs token) for a
+    specific user device so that document-processing events can be forwarded
+    as push notifications to the native mobile app.
+    """
+
+    __tablename__ = "mobile_devices"
+
+    id = Column(Integer, primary_key=True, index=True)
+
+    # User that owns this device registration.
+    owner_id = Column(String, nullable=False, index=True)
+
+    # Human-readable name the user gave this device (e.g. "John's iPhone").
+    device_name = Column(String(255), nullable=True)
+
+    # Platform: "ios", "android", or "web".
+    platform = Column(String(20), nullable=False, default="ios")
+
+    # Expo push token (ExponentPushToken[…]) or raw FCM/APNs token.
+    push_token = Column(String(512), nullable=False)
+
+    # Whether push notifications are enabled for this device.
+    is_active = Column(Boolean, nullable=False, default=True)
+
+    # Timestamps.
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    last_seen_at = Column(DateTime(timezone=True), nullable=True)
+
+    __table_args__ = (UniqueConstraint("owner_id", "push_token", name="uq_mobile_device_owner_token"),)
+
+
 class ComplianceTemplate(Base):
     """Pre-built compliance configuration templates (GDPR, HIPAA, SOC2).