Add multi-tenancy with Teams feature

Implement team-based organization for projects with role-based access control:

Backend:
- Add teams and team_memberships database tables (migrations 009, 009b)
- Add Team and TeamMembership ORM models with relationships
- Implement TeamAuthorizationService for team-level access control
- Add team CRUD, membership, and projects API endpoints
- Update project creation to support team assignment

Frontend:
- Add TeamContext for managing team state with localStorage persistence
- Add TeamSelector component for switching between teams
- Add TeamsPage, TeamDashboardPage, TeamSettingsPage, TeamMembersPage
- Add team API client functions
- Update navigation with Teams link

Security:
- Team role hierarchy: owner > admin > member
- Membership checked before system admin fallback
- Self-modification prevention for role changes
- Email visibility restricted to team admins/owners
- Slug validation rejects consecutive hyphens

Tests:
- Unit tests for TeamAuthorizationService
- Integration tests for all team API endpoints

frontend/src/api.ts

@@ -36,6 +36,12 @@ import {
   ArtifactDependenciesResponse,
   ReverseDependenciesResponse,
   DependencyResolutionResponse,
+  TeamDetail,
+  TeamMember,
+  TeamCreate,
+  TeamUpdate,
+  TeamMemberCreate,
+  TeamMemberUpdate,
 } from './types';
 
 const API_BASE = '/api/v1';
@@ -562,3 +568,103 @@ export async function getEnsureFile(
   }
   return response.text();
 }
+
+// Team API
+export async function listTeams(params: ListParams = {}): Promise<PaginatedResponse<TeamDetail>> {
+  const query = buildQueryString(params as Record<string, unknown>);
+  const response = await fetch(`${API_BASE}/teams${query}`, {
+    credentials: 'include',
+  });
+  return handleResponse<PaginatedResponse<TeamDetail>>(response);
+}
+
+export async function createTeam(data: TeamCreate): Promise<TeamDetail> {
+  const response = await fetch(`${API_BASE}/teams`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(data),
+    credentials: 'include',
+  });
+  return handleResponse<TeamDetail>(response);
+}
+
+export async function getTeam(slug: string): Promise<TeamDetail> {
+  const response = await fetch(`${API_BASE}/teams/${slug}`, {
+    credentials: 'include',
+  });
+  return handleResponse<TeamDetail>(response);
+}
+
+export async function updateTeam(slug: string, data: TeamUpdate): Promise<TeamDetail> {
+  const response = await fetch(`${API_BASE}/teams/${slug}`, {
+    method: 'PUT',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(data),
+    credentials: 'include',
+  });
+  return handleResponse<TeamDetail>(response);
+}
+
+export async function deleteTeam(slug: string): Promise<void> {
+  const response = await fetch(`${API_BASE}/teams/${slug}`, {
+    method: 'DELETE',
+    credentials: 'include',
+  });
+  if (!response.ok) {
+    const error = await response.json().catch(() => ({ detail: 'Unknown error' }));
+    throw new ApiError(error.detail || `HTTP ${response.status}`, response.status);
+  }
+}
+
+export async function listTeamMembers(slug: string): Promise<TeamMember[]> {
+  const response = await fetch(`${API_BASE}/teams/${slug}/members`, {
+    credentials: 'include',
+  });
+  return handleResponse<TeamMember[]>(response);
+}
+
+export async function addTeamMember(slug: string, data: TeamMemberCreate): Promise<TeamMember> {
+  const response = await fetch(`${API_BASE}/teams/${slug}/members`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(data),
+    credentials: 'include',
+  });
+  return handleResponse<TeamMember>(response);
+}
+
+export async function updateTeamMember(
+  slug: string,
+  username: string,
+  data: TeamMemberUpdate
+): Promise<TeamMember> {
+  const response = await fetch(`${API_BASE}/teams/${slug}/members/${username}`, {
+    method: 'PUT',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(data),
+    credentials: 'include',
+  });
+  return handleResponse<TeamMember>(response);
+}
+
+export async function removeTeamMember(slug: string, username: string): Promise<void> {
+  const response = await fetch(`${API_BASE}/teams/${slug}/members/${username}`, {
+    method: 'DELETE',
+    credentials: 'include',
+  });
+  if (!response.ok) {
+    const error = await response.json().catch(() => ({ detail: 'Unknown error' }));
+    throw new ApiError(error.detail || `HTTP ${response.status}`, response.status);
+  }
+}
+
+export async function listTeamProjects(
+  slug: string,
+  params: ProjectListParams = {}
+): Promise<PaginatedResponse<Project>> {
+  const query = buildQueryString(params as Record<string, unknown>);
+  const response = await fetch(`${API_BASE}/teams/${slug}/projects${query}`, {
+    credentials: 'include',
+  });
+  return handleResponse<PaginatedResponse<Project>>(response);
+}