Phase 6: Admin portal

Adds is_site_admin-gated site administration: user management (list,
deactivate/reactivate, reset password, promote/demote), room management
(list all rooms including private ones, archive/unarchive, force-transfer
ownership), and an audit log of every admin action.

Backend: User.is_active (deactivation) and Room.is_archived (archive) are
new columns; AdminAuditLog is a new table matching ARCHITECTURE.md's
admin_audit_log design, written to in the same transaction as every
mutating admin action. require_site_admin (dependencies.py) gates all
/api/admin/* routes. get_current_user now rechecks is_active on every
request, so deactivating a user kills their already-open session
immediately, not just future logins. An admin can't deactivate or demote
their own account (the one self-lockout guard included). Archived rooms
drop out of the open-room browse list but stay readable for existing
members.

Frontend: new /admin route (AdminRoute guard, redirects non-admins to
/rooms) with a tabbed Users / Rooms / Audit log / Settings page, plus an
"Admin" link in the account menu for site admins.

Bot/integration management and system settings -- both listed in the
original issue -- are intentionally not here: bot management has nothing
to manage until Phase 7 builds the actual bot data model, and there's no
settings storage or concrete setting to configure yet. Settings has an
empty placeholder tab; bot management is deferred entirely to Phase 7.
Confirmed this scope cut with the repo owner before implementing.

New tests/test_admin.py (14 tests, full suite now 58/58) covers every
admin endpoint's permission gate, the self-action guards, deactivation's
immediate effect on an already-open session, and that every mutating
action produces exactly one audit log row.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -1,3 +1,4 @@
+from app.models.admin_audit_log import AdminAuditLog
 from app.models.base import Base
 from app.models.invite import InviteStatus, RoomInvite
 from app.models.membership import RoomMembership, RoomRole
@@ -16,4 +17,5 @@ __all__ = [
     "RoomInvite",
     "InviteStatus",
     "PushSubscription",
+    "AdminAuditLog",
 ]

backend/app/models/admin_audit_log.py

@@ -0,0 +1,24 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, String, func
+from sqlalchemy.dialects.postgresql import JSONB
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import Base
+
+
+class AdminAuditLog(Base):
+    __tablename__ = "admin_audit_log"
+
+    id: Mapped[uuid.UUID] = mapped_column(primary_key=True, default=uuid.uuid4)
+    actor_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("users.id"), index=True, nullable=False)
+    action: Mapped[str] = mapped_column(String(100), nullable=False)
+    target_type: Mapped[str] = mapped_column(String(50), nullable=False)
+    target_id: Mapped[uuid.UUID] = mapped_column(nullable=False)
+    metadata_: Mapped[dict | None] = mapped_column("metadata", JSONB)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), nullable=False, index=True
+    )
+
+    actor = relationship("User")

backend/app/models/room.py

@@ -14,6 +14,7 @@ class Room(Base):
     name: Mapped[str] = mapped_column(String(100), unique=True, index=True, nullable=False)
     description: Mapped[str | None] = mapped_column(Text)
     is_private: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
+    is_archived: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
     owner_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("users.id"), nullable=False)
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), server_default=func.now(), nullable=False

backend/app/models/user.py

@@ -16,6 +16,7 @@ class User(Base):
     password_hash: Mapped[str] = mapped_column(String(255), nullable=False)
     is_bot: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
     is_site_admin: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
+    is_active: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), server_default=func.now(), nullable=False
     )