fix: standardize rate limit headers and remove dead code

- Use rateLimitHeaders() spread on /api/posts success response
  to include X-RateLimit-Limit, X-RateLimit-Reset, Retry-After
  matching /api/search and /api/search/suggestions behavior
- Remove legacy checkRateLimit, RateLimitResult, rateLimitStore,
  and cleanup interval from src/lib/search.ts (dead code after
  migration to central searchLimiter)
- Update tests to use searchLimiter from @/lib/security instead
  of the removed checkRateLimit

All integration tests pass (20 passed, 12 skipped).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/app/(frontend)/api/posts/route.ts

@@ -134,7 +134,7 @@ export async function GET(request: NextRequest) {
 
     return NextResponse.json(response, {
       headers: {
-        'X-RateLimit-Remaining': String(rateLimit.remaining),
+        ...rateLimitHeaders(rateLimit, POSTS_RATE_LIMIT),
         'Cache-Control': 'public, max-age=60, s-maxage=60',
       },
     })

src/lib/search.ts

@@ -79,12 +79,6 @@ export interface PaginatedPosts {
   hasPrevPage: boolean
 }
 
-export interface RateLimitResult {
-  allowed: boolean
-  remaining: number
-  retryAfter?: number
-}
-
 // ============================================================================
 // TTL Cache Implementation
 // ============================================================================
@@ -154,48 +148,6 @@ class TTLCache<K, V> {
 export const searchCache = new TTLCache<string, SearchResult>(60)
 export const suggestionCache = new TTLCache<string, Suggestion[]>(60)
 
-// ============================================================================
-// Rate Limiting
-// ============================================================================
-
-interface RateLimitEntry {
-  count: number
-  windowStart: number
-}
-
-const rateLimitStore = new Map<string, RateLimitEntry>()
-const RATE_LIMIT_WINDOW_MS = 60000 // 1 minute
-const RATE_LIMIT_MAX_REQUESTS = 30 // 30 requests per minute
-
-// Cleanup rate limit entries every 5 minutes
-setInterval(() => {
-  const now = Date.now()
-  for (const [key, entry] of rateLimitStore.entries()) {
-    if (now - entry.windowStart > RATE_LIMIT_WINDOW_MS * 2) {
-      rateLimitStore.delete(key)
-    }
-  }
-}, 300000)
-
-export function checkRateLimit(ip: string): RateLimitResult {
-  const now = Date.now()
-  const entry = rateLimitStore.get(ip)
-
-  if (!entry || now - entry.windowStart > RATE_LIMIT_WINDOW_MS) {
-    // New window
-    rateLimitStore.set(ip, { count: 1, windowStart: now })
-    return { allowed: true, remaining: RATE_LIMIT_MAX_REQUESTS - 1 }
-  }
-
-  if (entry.count >= RATE_LIMIT_MAX_REQUESTS) {
-    const retryAfter = Math.ceil((entry.windowStart + RATE_LIMIT_WINDOW_MS - now) / 1000)
-    return { allowed: false, remaining: 0, retryAfter }
-  }
-
-  entry.count++
-  return { allowed: true, remaining: RATE_LIMIT_MAX_REQUESTS - entry.count }
-}
-
 // ============================================================================
 // Helper Functions
 // ============================================================================

tests/int/search.int.spec.ts

@@ -5,11 +5,11 @@ import {
   searchPosts,
   getSearchSuggestions,
   getPostsByCategory,
-  checkRateLimit,
   searchCache,
   suggestionCache,
   extractTextFromLexical,
 } from '@/lib/search'
+import { searchLimiter } from '@/lib/security'
 
 let payload: Payload
 
@@ -78,24 +78,24 @@ describe('Search Library', () => {
     })
   })
 
-  describe('checkRateLimit', () => {
-    it('allows requests within limit', () => {
+  describe('searchLimiter (central rate limiter)', () => {
+    it('allows requests within limit', async () => {
       const testIp = `test-${Date.now()}-1`
-      const result = checkRateLimit(testIp)
+      const result = await searchLimiter.check(testIp)
 
       expect(result.allowed).toBe(true)
       expect(result.remaining).toBe(29) // 30 - 1
     })
 
-    it('blocks requests exceeding limit', () => {
+    it('blocks requests exceeding limit', async () => {
       const testIp = `test-${Date.now()}-2`
 
       // Use up all requests
       for (let i = 0; i < 30; i++) {
-        checkRateLimit(testIp)
+        await searchLimiter.check(testIp)
       }
 
-      const result = checkRateLimit(testIp)
+      const result = await searchLimiter.check(testIp)
       expect(result.allowed).toBe(false)
       expect(result.remaining).toBe(0)
       expect(result.retryAfter).toBeGreaterThan(0)