feat: add Agent Skills and restructure documentation

- Add 47 Agent Skills across 14 plugins following Anthropic's specification
  - Python (5): async patterns, testing, packaging, performance, UV package manager
  - JavaScript/TypeScript (4): advanced types, Node.js patterns, testing, modern JS
  - Kubernetes (4): manifests, Helm charts, GitOps, security policies
  - Cloud Infrastructure (4): Terraform, multi-cloud, hybrid networking, cost optimization
  - CI/CD (4): pipeline design, GitHub Actions, GitLab CI, secrets management
  - Backend (3): API design, architecture patterns, microservices
  - LLM Applications (4): LangChain, prompt engineering, RAG, evaluation
  - Blockchain/Web3 (4): DeFi protocols, NFT standards, Solidity security, Web3 testing
  - Framework Migration (4): React, Angular, database, dependency upgrades
  - Observability (4): Prometheus, Grafana, distributed tracing, SLO
  - Payment Processing (4): Stripe, PayPal, PCI compliance, billing
  - API Scaffolding (1): FastAPI templates
  - ML Operations (1): ML pipeline workflow
  - Security (1): SAST configuration

- Restructure documentation into /docs directory
  - agent-skills.md: Complete guide to all 47 skills
  - agents.md: All 85 agents with model configuration
  - plugins.md: Complete catalog of 63 plugins
  - usage.md: Commands, workflows, and best practices
  - architecture.md: Design principles and patterns

- Update README.md
  - Add Agent Skills banner announcement
  - Reduce length by ~75% with links to detailed docs
  - Add What's New section showcasing Agent Skills
  - Add Popular Use Cases with real examples
  - Improve navigation with Core Guides and Quick Links

- Update marketplace.json with skills arrays for 14 plugins

All 47 skills follow Agent Skills Specification:
- Required YAML frontmatter (name, description)
- Use when activation clauses
- Progressive disclosure architecture
- Under 1024 character descriptions

plugins/backend-development/skills/api-design-principles/assets/rest-api-template.py

@@ -0,0 +1,165 @@
+"""
+Production-ready REST API template using FastAPI.
+Includes pagination, filtering, error handling, and best practices.
+"""
+
+from fastapi import FastAPI, HTTPException, Query, Path, Depends, status
+from fastapi.responses import JSONResponse
+from pydantic import BaseModel, Field, EmailStr
+from typing import Optional, List, Any
+from datetime import datetime
+from enum import Enum
+
+app = FastAPI(
+    title="API Template",
+    version="1.0.0",
+    docs_url="/api/docs"
+)
+
+# Models
+class UserStatus(str, Enum):
+    ACTIVE = "active"
+    INACTIVE = "inactive"
+    SUSPENDED = "suspended"
+
+class UserBase(BaseModel):
+    email: EmailStr
+    name: str = Field(..., min_length=1, max_length=100)
+    status: UserStatus = UserStatus.ACTIVE
+
+class UserCreate(UserBase):
+    password: str = Field(..., min_length=8)
+
+class UserUpdate(BaseModel):
+    email: Optional[EmailStr] = None
+    name: Optional[str] = Field(None, min_length=1, max_length=100)
+    status: Optional[UserStatus] = None
+
+class User(UserBase):
+    id: str
+    created_at: datetime
+    updated_at: datetime
+
+    class Config:
+        from_attributes = True
+
+# Pagination
+class PaginationParams(BaseModel):
+    page: int = Field(1, ge=1)
+    page_size: int = Field(20, ge=1, le=100)
+
+class PaginatedResponse(BaseModel):
+    items: List[Any]
+    total: int
+    page: int
+    page_size: int
+    pages: int
+
+# Error handling
+class ErrorDetail(BaseModel):
+    field: Optional[str] = None
+    message: str
+    code: str
+
+class ErrorResponse(BaseModel):
+    error: str
+    message: str
+    details: Optional[List[ErrorDetail]] = None
+
+@app.exception_handler(HTTPException)
+async def http_exception_handler(request, exc):
+    return JSONResponse(
+        status_code=exc.status_code,
+        content=ErrorResponse(
+            error=exc.__class__.__name__,
+            message=exc.detail if isinstance(exc.detail, str) else exc.detail.get("message", "Error"),
+            details=exc.detail.get("details") if isinstance(exc.detail, dict) else None
+        ).dict()
+    )
+
+# Endpoints
+@app.get("/api/users", response_model=PaginatedResponse, tags=["Users"])
+async def list_users(
+    page: int = Query(1, ge=1),
+    page_size: int = Query(20, ge=1, le=100),
+    status: Optional[UserStatus] = Query(None),
+    search: Optional[str] = Query(None)
+):
+    """List users with pagination and filtering."""
+    # Mock implementation
+    total = 100
+    items = [
+        User(
+            id=str(i),
+            email=f"user{i}@example.com",
+            name=f"User {i}",
+            status=UserStatus.ACTIVE,
+            created_at=datetime.now(),
+            updated_at=datetime.now()
+        ).dict()
+        for i in range((page-1)*page_size, min(page*page_size, total))
+    ]
+
+    return PaginatedResponse(
+        items=items,
+        total=total,
+        page=page,
+        page_size=page_size,
+        pages=(total + page_size - 1) // page_size
+    )
+
+@app.post("/api/users", response_model=User, status_code=status.HTTP_201_CREATED, tags=["Users"])
+async def create_user(user: UserCreate):
+    """Create a new user."""
+    # Mock implementation
+    return User(
+        id="123",
+        email=user.email,
+        name=user.name,
+        status=user.status,
+        created_at=datetime.now(),
+        updated_at=datetime.now()
+    )
+
+@app.get("/api/users/{user_id}", response_model=User, tags=["Users"])
+async def get_user(user_id: str = Path(..., description="User ID")):
+    """Get user by ID."""
+    # Mock: Check if exists
+    if user_id == "999":
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail={"message": "User not found", "details": {"id": user_id}}
+        )
+
+    return User(
+        id=user_id,
+        email="user@example.com",
+        name="User Name",
+        status=UserStatus.ACTIVE,
+        created_at=datetime.now(),
+        updated_at=datetime.now()
+    )
+
+@app.patch("/api/users/{user_id}", response_model=User, tags=["Users"])
+async def update_user(user_id: str, update: UserUpdate):
+    """Partially update user."""
+    # Validate user exists
+    existing = await get_user(user_id)
+
+    # Apply updates
+    update_data = update.dict(exclude_unset=True)
+    for field, value in update_data.items():
+        setattr(existing, field, value)
+
+    existing.updated_at = datetime.now()
+    return existing
+
+@app.delete("/api/users/{user_id}", status_code=status.HTTP_204_NO_CONTENT, tags=["Users"])
+async def delete_user(user_id: str):
+    """Delete user."""
+    await get_user(user_id)  # Verify exists
+    return None
+
+if __name__ == "__main__":
+    import uvicorn
+    uvicorn.run(app, host="0.0.0.0", port=8000)