feat: Expand fleet to 23 skills across all domains

New skills (14):
- nestjs-best-practices: 40 priority-ranked rules (kadajett)
- fastapi: Pydantic v2, async SQLAlchemy, JWT auth (jezweb)
- architecture-patterns: Clean Architecture, Hexagonal, DDD (wshobson)
- python-performance-optimization: Profiling and optimization (wshobson)
- ai-sdk: Vercel AI SDK streaming and agent patterns (vercel)
- create-agent: Modular agent architecture with OpenRouter (openrouterteam)
- proactive-agent: WAL Protocol, compaction recovery, self-improvement (halthelobster)
- brand-guidelines: Brand identity enforcement (anthropics)
- ui-animation: Motion design with accessibility (mblode)
- marketing-ideas: 139 ideas across 14 categories (coreyhaines31)
- pricing-strategy: SaaS pricing and tier design (coreyhaines31)
- programmatic-seo: SEO at scale with playbooks (coreyhaines31)
- competitor-alternatives: Comparison page architecture (coreyhaines31)
- referral-program: Referral and affiliate programs (coreyhaines31)

README reorganized by domain: Code Quality, Frontend, Backend,
Auth, AI/Agent Building, Marketing, Design, Meta.

Mosaic Stack is not limited to coding — the Orchestrator serves
coding, business, design, marketing, writing, logistics, and analysis.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

skills/nestjs-best-practices/rules/error-throw-http-exceptions.md

@@ -0,0 +1,114 @@
+---
+title: Throw HTTP Exceptions from Services
+impact: HIGH
+impactDescription: Keeps controllers thin and simplifies error handling
+tags: error-handling, exceptions, services
+---
+
+## Throw HTTP Exceptions from Services
+
+It's acceptable (and often preferable) to throw `HttpException` subclasses from services in HTTP applications. This keeps controllers thin and allows services to communicate appropriate error states. For truly layer-agnostic services, use domain exceptions that map to HTTP status codes.
+
+**Incorrect (return error objects instead of throwing):**
+
+```typescript
+// Return error objects instead of throwing
+@Injectable()
+export class UsersService {
+  async findById(id: string): Promise<{ user?: User; error?: string }> {
+    const user = await this.repo.findOne({ where: { id } });
+    if (!user) {
+      return { error: 'User not found' }; // Controller must check this
+    }
+    return { user };
+  }
+}
+
+@Controller('users')
+export class UsersController {
+  @Get(':id')
+  async findOne(@Param('id') id: string) {
+    const result = await this.usersService.findById(id);
+    if (result.error) {
+      throw new NotFoundException(result.error);
+    }
+    return result.user;
+  }
+}
+```
+
+**Correct (throw exceptions directly from service):**
+
+```typescript
+// Throw exceptions directly from service
+@Injectable()
+export class UsersService {
+  constructor(private readonly repo: UserRepository) {}
+
+  async findById(id: string): Promise<User> {
+    const user = await this.repo.findOne({ where: { id } });
+    if (!user) {
+      throw new NotFoundException(`User #${id} not found`);
+    }
+    return user;
+  }
+
+  async create(dto: CreateUserDto): Promise<User> {
+    const existing = await this.repo.findOne({
+      where: { email: dto.email },
+    });
+    if (existing) {
+      throw new ConflictException('Email already registered');
+    }
+    return this.repo.save(dto);
+  }
+
+  async update(id: string, dto: UpdateUserDto): Promise<User> {
+    const user = await this.findById(id); // Throws if not found
+    Object.assign(user, dto);
+    return this.repo.save(user);
+  }
+}
+
+// Controller stays thin
+@Controller('users')
+export class UsersController {
+  @Get(':id')
+  findOne(@Param('id') id: string): Promise<User> {
+    return this.usersService.findById(id);
+  }
+
+  @Post()
+  create(@Body() dto: CreateUserDto): Promise<User> {
+    return this.usersService.create(dto);
+  }
+}
+
+// For layer-agnostic services, use domain exceptions
+export class EntityNotFoundException extends Error {
+  constructor(
+    public readonly entity: string,
+    public readonly id: string,
+  ) {
+    super(`${entity} with ID "${id}" not found`);
+  }
+}
+
+// Map to HTTP in exception filter
+@Catch(EntityNotFoundException)
+export class EntityNotFoundFilter implements ExceptionFilter {
+  catch(exception: EntityNotFoundException, host: ArgumentsHost) {
+    const ctx = host.switchToHttp();
+    const response = ctx.getResponse<Response>();
+
+    response.status(404).json({
+      statusCode: 404,
+      message: exception.message,
+      entity: exception.entity,
+      id: exception.id,
+    });
+  }
+}
+```
+
+Reference: [NestJS Exception Filters](https://docs.nestjs.com/exception-filters)