Add new skills for backend patterns, coding standards, continuous learning, and NestJS best practices

- Introduced backend patterns skill with guidelines on API design, database optimization, and server-side best practices.
- Added coding standards skill outlining universal coding principles for TypeScript, NestJS, and Node.js development.
- Implemented continuous learning skill to automatically extract reusable patterns from Cursor sessions.
- Created NestJS best practices skill detailing architecture patterns, dependency injection, error handling, and security measures.
- Included various rules and templates for NestJS best practices to ensure production-ready applications.

.agents/skills/nestjs-best-practices/rules/db-use-migrations.md

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+---
+title: Use Database Migrations
+impact: HIGH
+impactDescription: Enables safe, repeatable database schema changes
+tags: database, migrations, drizzle, schema
+---
+
+## Use Database Migrations
+
+Never push schema changes with `drizzle-kit push` in production. Use versioned SQL migrations for all schema changes. Migrations provide version control for your database, enable safe rollbacks, and ensure consistency across all environments.
+
+**Incorrect (pushing schema or running ad-hoc SQL):**
+
+```typescript
+// drizzle-kit push against production
+// Mutates the live database with no rollback file
+
+@Injectable()
+export class DatabaseService {
+  async addColumn(): Promise<void> {
+    await this.db.execute(sql`ALTER TABLE users ADD COLUMN age INT`);
+  }
+}
+```
+
+**Correct (generate and apply Drizzle migrations):**
+
+```typescript
+// drizzle.config.ts
+import { defineConfig } from 'drizzle-kit';
+
+export default defineConfig({
+  schema: './drizzle/schema.ts',
+  out: './drizzle/migrations',
+  dialect: 'postgresql',
+  dbCredentials: {
+    url: process.env.DATABASE_URL!,
+  },
+});
+```
+
+```bash
+# Generate a migration from schema diffs
+npx drizzle-kit generate
+
+# Apply migrations
+npx drizzle-kit migrate
+```
+
+```typescript
+// drizzle/schema.ts
+export const users = pgTable('users', {
+  id: uuid('id').primaryKey().defaultRandom(),
+  email: varchar('email', { length: 255 }).notNull(),
+  age: integer('age').default(0),
+});
+```
+
+Always keep `down`/rollback SQL when a migration is destructive. Never edit an already-applied migration file; add a new one.
+
+Reference: [Drizzle Kit Migrations](https://orm.drizzle.team/docs/kit-overview)