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/api/endpoints/admin_dashboard.py

@@ -0,0 +1,82 @@
+from typing import Annotated
+from fastapi import APIRouter, Depends
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select, func
+
+from app.core.database import get_db
+from app.models.user import User
+from app.models.subscription import Subscription
+from app.models.tree import Tree
+from app.models.audit_log import AuditLog
+from app.schemas.admin import DashboardMetrics, ActivityEntry
+from app.api.deps import require_admin
+
+router = APIRouter(prefix="/admin/dashboard", tags=["admin-dashboard"])
+
+
+@router.get("/metrics", response_model=DashboardMetrics)
+async def get_dashboard_metrics(
+    db: Annotated[AsyncSession, Depends(get_db)],
+    current_user: Annotated[User, Depends(require_admin)],
+):
+    """Get platform overview metrics."""
+    total_users = await db.scalar(select(func.count()).select_from(User)) or 0
+    active_subs = await db.scalar(
+        select(func.count()).select_from(Subscription).where(
+            Subscription.status.in_(["active", "trialing"])
+        )
+    ) or 0
+    paid_accounts = await db.scalar(
+        select(func.count()).select_from(Subscription).where(
+            Subscription.plan.in_(["pro", "team"])
+        )
+    ) or 0
+    total_trees = await db.scalar(
+        select(func.count()).select_from(Tree).where(Tree.deleted_at.is_(None))
+    ) or 0
+
+    return DashboardMetrics(
+        total_users=total_users,
+        active_subscriptions=active_subs,
+        paid_accounts=paid_accounts,
+        total_trees=total_trees,
+    )
+
+
+@router.get("/activity", response_model=list[ActivityEntry])
+async def get_dashboard_activity(
+    db: Annotated[AsyncSession, Depends(get_db)],
+    current_user: Annotated[User, Depends(require_admin)],
+):
+    """Get recent audit log entries for activity feed."""
+    query = (
+        select(
+            AuditLog.id,
+            AuditLog.action,
+            AuditLog.resource_type,
+            AuditLog.resource_id,
+            AuditLog.details,
+            AuditLog.ip_address,
+            AuditLog.created_at,
+            User.email.label("user_email"),
+        )
+        .outerjoin(User, AuditLog.user_id == User.id)
+        .order_by(AuditLog.created_at.desc())
+        .limit(10)
+    )
+    result = await db.execute(query)
+    rows = result.all()
+
+    return [
+        ActivityEntry(
+            id=row.id,
+            user_email=row.user_email,
+            action=row.action,
+            resource_type=row.resource_type,
+            resource_id=row.resource_id,
+            details=row.details,
+            ip_address=row.ip_address,
+            created_at=row.created_at,
+        )
+        for row in rows
+    ]