feat(#2): Implement PostgreSQL 17 + pgvector database schema

Establishes multi-tenant database layer with vector similarity search for AI-powered memory features. Includes Docker infrastructure, Prisma ORM integration, NestJS services, and shared types across the monorepo.

Key changes:
- Docker: PostgreSQL 17 + pgvector v0.7.4, Valkey cache
- Schema: 8 models (User, Workspace, Task, Event, Project, ActivityLog, MemoryEmbedding) with RLS preparation
- NestJS: PrismaModule, DatabaseModule, EmbeddingsService
- Shared: Type-safe enums, constants, and database types

Fixes #2

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/api/prisma/seed.ts

@@ -0,0 +1,153 @@
+import {
+  PrismaClient,
+  TaskStatus,
+  TaskPriority,
+  ProjectStatus,
+  WorkspaceMemberRole,
+} from "@prisma/client";
+
+const prisma = new PrismaClient();
+
+async function main() {
+  console.log("Seeding database...");
+
+  // Create test user
+  const user = await prisma.user.upsert({
+    where: { email: "dev@mosaic.local" },
+    update: {},
+    create: {
+      email: "dev@mosaic.local",
+      name: "Development User",
+      preferences: {
+        theme: "system",
+        notifications: true,
+      },
+    },
+  });
+
+  console.log(`Created user: ${user.email}`);
+
+  // Create workspace
+  const workspace = await prisma.workspace.upsert({
+    where: { id: "00000000-0000-0000-0000-000000000001" },
+    update: {},
+    create: {
+      id: "00000000-0000-0000-0000-000000000001",
+      name: "Development Workspace",
+      ownerId: user.id,
+      settings: {
+        timezone: "America/New_York",
+      },
+    },
+  });
+
+  console.log(`Created workspace: ${workspace.name}`);
+
+  // Add user as workspace owner
+  await prisma.workspaceMember.upsert({
+    where: {
+      workspaceId_userId: {
+        workspaceId: workspace.id,
+        userId: user.id,
+      },
+    },
+    update: {},
+    create: {
+      workspaceId: workspace.id,
+      userId: user.id,
+      role: WorkspaceMemberRole.OWNER,
+    },
+  });
+
+  // Delete existing seed data for idempotency (avoids duplicates on re-run)
+  await prisma.task.deleteMany({ where: { workspaceId: workspace.id } });
+  await prisma.event.deleteMany({ where: { workspaceId: workspace.id } });
+  await prisma.project.deleteMany({ where: { workspaceId: workspace.id } });
+
+  // Create sample project
+  const project = await prisma.project.create({
+    data: {
+      workspaceId: workspace.id,
+      name: "Sample Project",
+      description: "A sample project for development",
+      status: ProjectStatus.ACTIVE,
+      creatorId: user.id,
+      color: "#3B82F6",
+    },
+  });
+
+  console.log(`Created project: ${project.name}`);
+
+  // Create sample tasks
+  const tasks = [
+    {
+      title: "Set up development environment",
+      status: TaskStatus.COMPLETED,
+      priority: TaskPriority.HIGH,
+    },
+    {
+      title: "Review project requirements",
+      status: TaskStatus.IN_PROGRESS,
+      priority: TaskPriority.MEDIUM,
+    },
+    {
+      title: "Design database schema",
+      status: TaskStatus.COMPLETED,
+      priority: TaskPriority.HIGH,
+    },
+    {
+      title: "Implement NestJS integration",
+      status: TaskStatus.COMPLETED,
+      priority: TaskPriority.HIGH,
+    },
+    {
+      title: "Create seed data",
+      status: TaskStatus.IN_PROGRESS,
+      priority: TaskPriority.MEDIUM,
+    },
+  ];
+
+  for (const taskData of tasks) {
+    await prisma.task.create({
+      data: {
+        workspaceId: workspace.id,
+        title: taskData.title,
+        status: taskData.status,
+        priority: taskData.priority,
+        creatorId: user.id,
+        projectId: project.id,
+      },
+    });
+  }
+
+  console.log(`Created ${tasks.length} sample tasks`);
+
+  // Create sample event
+  const tomorrow = new Date();
+  tomorrow.setDate(tomorrow.getDate() + 1);
+  tomorrow.setHours(10, 0, 0, 0);
+
+  await prisma.event.create({
+    data: {
+      workspaceId: workspace.id,
+      title: "Morning standup",
+      description: "Daily team sync",
+      startTime: tomorrow,
+      endTime: new Date(tomorrow.getTime() + 30 * 60000), // 30 minutes later
+      creatorId: user.id,
+      projectId: project.id,
+    },
+  });
+
+  console.log("Created sample event");
+  console.log("Seeding completed successfully!");
+}
+
+main()
+  .catch((e) => {
+    console.error("Error seeding database:", e);
+    process.exit(1);
+  })
+  .finally(async () => {
+    await prisma.$disconnect();
+  });