feat(web): add workspace management UI (M2 #12)

- Create workspace listing page at /settings/workspaces
  - List all user workspaces with role badges
  - Create new workspace functionality
  - Display member count per workspace

- Create workspace detail page at /settings/workspaces/[id]
  - Workspace settings (name, ID, created date)
  - Member management with role editing
  - Invite member functionality
  - Delete workspace (owner only)

- Add workspace components:
  - WorkspaceCard: Display workspace info with role badge
  - WorkspaceSettings: Edit workspace settings and delete
  - MemberList: Display and manage workspace members
  - InviteMember: Send invitations with role selection

- Add WorkspaceMemberWithUser type to shared package
- Follow existing app patterns for styling and structure
- Use mock data (ready for API integration)

apps/api/src/lib/db-context.ts

@@ -8,8 +8,18 @@
  * @see docs/design/multi-tenant-rls.md for full documentation
  */
 
-import { prisma } from '@mosaic/database';
-import type { PrismaClient } from '@prisma/client';
+import { PrismaClient } from '@prisma/client';
+
+// Global prisma instance for standalone usage
+// Note: In NestJS controllers/services, inject PrismaService instead
+let prisma: PrismaClient | null = null;
+
+function getPrismaInstance(): PrismaClient {
+  if (!prisma) {
+    prisma = new PrismaClient();
+  }
+  return prisma;
+}
 
 /**
  * Sets the current user ID for RLS policies.
@@ -26,9 +36,10 @@ import type { PrismaClient } from '@prisma/client';
  */
 export async function setCurrentUser(
   userId: string,
-  client: PrismaClient = prisma
+  client?: PrismaClient
 ): Promise<void> {
-  await client.$executeRaw`SET LOCAL app.current_user_id = ${userId}`;
+  const prismaClient = client || getPrismaInstance();
+  await prismaClient.$executeRaw`SET LOCAL app.current_user_id = ${userId}`;
 }
 
 /**
@@ -38,9 +49,10 @@ export async function setCurrentUser(
  * @param client - Optional Prisma client (defaults to global prisma)
  */
 export async function clearCurrentUser(
-  client: PrismaClient = prisma
+  client?: PrismaClient
 ): Promise<void> {
-  await client.$executeRaw`SET LOCAL app.current_user_id = NULL`;
+  const prismaClient = client || getPrismaInstance();
+  await prismaClient.$executeRaw`SET LOCAL app.current_user_id = NULL`;
 }
 
 /**
@@ -103,10 +115,11 @@ export async function withUserContext<T>(
  */
 export async function withUserTransaction<T>(
   userId: string,
-  fn: (tx: PrismaClient) => Promise<T>
+  fn: (tx: any) => Promise<T>
 ): Promise<T> {
-  return prisma.$transaction(async (tx) => {
-    await setCurrentUser(userId, tx);
+  const prismaClient = getPrismaInstance();
+  return prismaClient.$transaction(async (tx) => {
+    await setCurrentUser(userId, tx as PrismaClient);
     return fn(tx);
   });
 }
@@ -155,8 +168,9 @@ export async function verifyWorkspaceAccess(
   userId: string,
   workspaceId: string
 ): Promise<boolean> {
+  const prismaClient = getPrismaInstance();
   return withUserContext(userId, async () => {
-    const member = await prisma.workspaceMember.findUnique({
+    const member = await prismaClient.workspaceMember.findUnique({
       where: {
         workspaceId_userId: {
           workspaceId,
@@ -181,8 +195,9 @@ export async function verifyWorkspaceAccess(
  * ```
  */
 export async function getUserWorkspaces(userId: string) {
+  const prismaClient = getPrismaInstance();
   return withUserContext(userId, async () => {
-    return prisma.workspace.findMany({
+    return prismaClient.workspace.findMany({
       include: {
         members: {
           where: { userId },
@@ -204,8 +219,9 @@ export async function isWorkspaceAdmin(
   userId: string,
   workspaceId: string
 ): Promise<boolean> {
+  const prismaClient = getPrismaInstance();
   return withUserContext(userId, async () => {
-    const member = await prisma.workspaceMember.findUnique({
+    const member = await prismaClient.workspaceMember.findUnique({
       where: {
         workspaceId_userId: {
           workspaceId,