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/schemas/admin.py

@@ -0,0 +1,208 @@
+"""Pydantic schemas for admin panel endpoints."""
+from datetime import datetime
+from typing import Optional
+from uuid import UUID
+from pydantic import BaseModel, Field
+
+
+# --- Dashboard ---
+
+class DashboardMetrics(BaseModel):
+    total_users: int
+    active_subscriptions: int
+    paid_accounts: int
+    total_trees: int
+
+
+class ActivityEntry(BaseModel):
+    id: UUID
+    user_email: Optional[str] = None
+    action: str
+    resource_type: str
+    resource_id: Optional[UUID] = None
+    details: Optional[dict] = None
+    ip_address: Optional[str] = None
+    created_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+# --- Audit Logs ---
+
+class AuditLogEntry(BaseModel):
+    id: UUID
+    user_id: UUID
+    user_email: Optional[str] = None
+    action: str
+    resource_type: str
+    resource_id: Optional[UUID] = None
+    details: Optional[dict] = None
+    ip_address: Optional[str] = None
+    created_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+class AuditLogListResponse(BaseModel):
+    items: list[AuditLogEntry]
+    total: int
+    page: int
+    per_page: int
+
+
+# --- Plan Limits ---
+
+class PlanLimitResponse(BaseModel):
+    plan: str
+    max_trees: Optional[int] = None
+    max_sessions_per_month: Optional[int] = None
+    max_users: Optional[int] = None
+    custom_branding: bool = False
+    priority_support: bool = False
+    export_formats: list = []
+
+    class Config:
+        from_attributes = True
+
+
+class PlanLimitUpdate(BaseModel):
+    plan: str
+    max_trees: Optional[int] = None
+    max_sessions_per_month: Optional[int] = None
+    max_users: Optional[int] = None
+    custom_branding: bool = False
+    priority_support: bool = False
+    export_formats: list = Field(default_factory=lambda: ["markdown", "text"])
+
+
+class AccountOverrideCreate(BaseModel):
+    account_display_code: str = Field(..., description="Account display code to look up")
+    override_max_trees: Optional[int] = None
+    override_max_sessions_per_month: Optional[int] = None
+    override_max_users: Optional[int] = None
+    note: Optional[str] = None
+
+
+class AccountOverrideUpdate(BaseModel):
+    override_max_trees: Optional[int] = None
+    override_max_sessions_per_month: Optional[int] = None
+    override_max_users: Optional[int] = None
+    note: Optional[str] = None
+
+
+class AccountOverrideResponse(BaseModel):
+    id: UUID
+    account_id: UUID
+    account_name: Optional[str] = None
+    account_display_code: Optional[str] = None
+    override_max_trees: Optional[int] = None
+    override_max_sessions_per_month: Optional[int] = None
+    override_max_users: Optional[int] = None
+    note: Optional[str] = None
+    created_at: datetime
+    updated_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+# --- Feature Flags ---
+
+class FeatureFlagCreate(BaseModel):
+    flag_key: str = Field(..., max_length=100)
+    display_name: str = Field(..., max_length=255)
+    description: Optional[str] = None
+
+
+class FeatureFlagUpdate(BaseModel):
+    display_name: Optional[str] = None
+    description: Optional[str] = None
+
+
+class PlanDefaultEntry(BaseModel):
+    plan: str
+    enabled: bool
+
+
+class FeatureFlagResponse(BaseModel):
+    id: UUID
+    flag_key: str
+    display_name: str
+    description: Optional[str] = None
+    plan_defaults: list[PlanDefaultEntry] = []
+    created_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+class PlanDefaultUpdate(BaseModel):
+    plan: str
+    flag_id: UUID
+    enabled: bool
+
+
+class AccountFeatureOverrideCreate(BaseModel):
+    account_display_code: str
+    flag_id: UUID
+    enabled: bool
+    note: Optional[str] = None
+
+
+class AccountFeatureOverrideResponse(BaseModel):
+    id: UUID
+    account_id: UUID
+    account_display_code: Optional[str] = None
+    flag_id: UUID
+    flag_key: Optional[str] = None
+    flag_display_name: Optional[str] = None
+    enabled: bool
+    note: Optional[str] = None
+    created_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+# --- Platform Settings ---
+
+class SettingsResponse(BaseModel):
+    settings: dict
+
+
+class SettingsUpdate(BaseModel):
+    settings: dict = Field(..., description="Key-value pairs to update")
+
+
+# --- Global Categories ---
+
+class GlobalCategoryCreate(BaseModel):
+    name: str = Field(..., min_length=1, max_length=100)
+    slug: str = Field(..., min_length=1, max_length=100)
+    description: Optional[str] = None
+
+
+class GlobalCategoryUpdate(BaseModel):
+    name: Optional[str] = Field(None, max_length=100)
+    slug: Optional[str] = Field(None, max_length=100)
+    description: Optional[str] = None
+
+
+class GlobalCategoryResponse(BaseModel):
+    id: UUID
+    name: str
+    slug: str
+    description: Optional[str] = None
+    account_id: Optional[UUID] = None
+    tree_count: int = 0
+
+    class Config:
+        from_attributes = True
+
+
+# --- Move User ---
+
+class MoveUserAccount(BaseModel):
+    display_code: str = Field(..., description="Target account display code")