feat: user management — admin create, password reset, archive/delete, quick invite

Phase 1: must_change_password enforcement + change password endpoint/page
Phase 2: Admin user creation (M365-style) with temp password
Phase 3: Password reset (self-service forgot + admin-triggered)
Phase 4: User archive (soft delete) + hard delete with precheck
Phase 5: Quick invite from admin Users page

Also fixes:
- Auto-create subscription for accounts missing one
- Hard delete precheck ignores sole-member personal accounts
- Seed script patches tree nodes for validation compliance

Migrations: 031 (must_change_password), 032 (password_reset_tokens), 033 (user soft delete)

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

backend/app/models/user.py

@@ -39,6 +39,7 @@ class User(Base):
     is_super_admin: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
     is_team_admin: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
     is_active: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True, server_default="true")
+    must_change_password: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, server_default="false")
 
     # Account-based multi-tenancy (new)
     account_id: Mapped[Optional[uuid.UUID]] = mapped_column(
@@ -66,6 +67,18 @@ class User(Base):
     )
     last_login: Mapped[Optional[datetime]] = mapped_column(DateTime(timezone=True), nullable=True)
 
+    # Soft delete
+    deleted_at: Mapped[Optional[datetime]] = mapped_column(
+        DateTime(timezone=True),
+        nullable=True,
+        index=True
+    )
+    deleted_by: Mapped[Optional[uuid.UUID]] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("users.id"),
+        nullable=True
+    )
+
     # Relationships
     account: Mapped[Optional["Account"]] = relationship("Account", foreign_keys=[account_id], back_populates="users")
     owned_account: Mapped[Optional["Account"]] = relationship("Account", foreign_keys="[Account.owner_id]", back_populates="owner", uselist=False)