feat: implement full admin panel with dashboard, user management, and platform settings

Adds complete super_admin panel with 9 pages and account owner categories page.
Backend includes 5 new DB tables, ~25 API endpoints, settings manager with
in-memory cache, and 29 integration tests. Frontend includes reusable admin
components (DataTable, Pagination, ActionMenu, etc.) with code-split lazy loading.

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

backend/app/models/account_limit_override.py

@@ -0,0 +1,42 @@
+import uuid
+from datetime import datetime, timezone
+from typing import Optional, TYPE_CHECKING
+from sqlalchemy import Integer, Text, DateTime, ForeignKey
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from sqlalchemy.dialects.postgresql import UUID
+from app.core.database import Base
+
+if TYPE_CHECKING:
+    from app.models.account import Account
+    from app.models.user import User
+
+
+class AccountLimitOverride(Base):
+    __tablename__ = "account_limit_overrides"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    account_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("accounts.id", ondelete="CASCADE"),
+        unique=True,
+        nullable=False
+    )
+    override_max_trees: Mapped[Optional[int]] = mapped_column(Integer, nullable=True)
+    override_max_sessions_per_month: Mapped[Optional[int]] = mapped_column(Integer, nullable=True)
+    override_max_users: Mapped[Optional[int]] = mapped_column(Integer, nullable=True)
+    note: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
+    created_by_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("users.id"),
+        nullable=False
+    )
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=lambda: datetime.now(timezone.utc))
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        default=lambda: datetime.now(timezone.utc),
+        onupdate=lambda: datetime.now(timezone.utc)
+    )
+
+    # Relationships
+    account: Mapped["Account"] = relationship("Account", back_populates="limit_override")
+    created_by: Mapped["User"] = relationship("User")