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>

turbo.json

@@ -1,8 +1,11 @@
 {
   "$schema": "https://turbo.build/schema.json",
   "tasks": {
+    "prisma:generate": {
+      "cache": false
+    },
     "build": {
-      "dependsOn": ["^build"],
+      "dependsOn": ["^build", "prisma:generate"],
       "outputs": ["dist/**", ".next/**", "!.next/cache/**"]
     },
     "dev": {