docs: salvage focused skill curation updates (#1723)

Port the safe, narrow pieces from contributor PR #1694 without taking the broad 11-skill rewrite.

- add drift-prone warnings to external research/media/API skills

- make search-first verify tool availability and use current agent naming

- remove unsafe in-memory rate limiter example from backend patterns

- tighten the CSP example in security-review

Validation: node scripts/ci/validate-skills.js --strict; npx markdownlint targeted skill files; node tests/ci/validators.test.js && node tests/ci/catalog.test.js; npm run lint; node tests/run-all.js

skills/backend-patterns/SKILL.md

@@ -430,51 +430,14 @@ export const DELETE = requirePermission('delete')(
 
 ## Rate Limiting
 
-### Simple In-Memory Rate Limiter
+Rate limiting must use a shared store such as Redis, a gateway, or the
+platform's native limiter. Do not use per-process in-memory counters for
+production APIs: they reset on deploy, split across replicas, and fail open in
+serverless or multi-instance environments.
 
-```typescript
-class RateLimiter {
-  private requests = new Map<string, number[]>()
-
-  async checkLimit(
-    identifier: string,
-    maxRequests: number,
-    windowMs: number
-  ): Promise<boolean> {
-    const now = Date.now()
-    const requests = this.requests.get(identifier) || []
-
-    // Remove old requests outside window
-    const recentRequests = requests.filter(time => now - time < windowMs)
-
-    if (recentRequests.length >= maxRequests) {
-      return false  // Rate limit exceeded
-    }
-
-    // Add current request
-    recentRequests.push(now)
-    this.requests.set(identifier, recentRequests)
-
-    return true
-  }
-}
-
-const limiter = new RateLimiter()
-
-export async function GET(request: Request) {
-  const ip = request.headers.get('x-forwarded-for') || 'unknown'
-
-  const allowed = await limiter.checkLimit(ip, 100, 60000)  // 100 req/min
-
-  if (!allowed) {
-    return NextResponse.json({
-      error: 'Rate limit exceeded'
-    }, { status: 429 })
-  }
-
-  // Continue with request
-}
-```
+Keep the backend layer responsible for choosing the integration point and error
+shape; use `api-design` for the HTTP contract and `security-review` for abuse
+case review.
 
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