refactor: dead-code cleanup + drop the lib/types shim (slice 9)

- Delete orphaned components (theme-provider, task-claim-button), the unused
  roleDisplayName helper, the fully-dead cleanupRateLimits, the 6 never-imported
  validation schemas (signIn/signUp/createSpace/joinSpace — a replaced auth flow;
  proposalStatuses; updateAreaLeadRoleSchema).
- Migrate all @/lib/types importers to the canonical @/types/domain and delete
  the compatibility shim.

tsc 0, 635 tests green, lint clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

lib/security.ts

@@ -139,18 +139,6 @@ export function checkRateLimit(
   return { allowed: true, remaining: maxRequests - entry.count, resetIn: entry.resetTime - now }
 }
 
-/**
- * Clear expired rate limit entries (call periodically)
- */
-export function cleanupRateLimits(): void {
-  const now = Date.now()
-  for (const [key, entry] of rateLimitStore.entries()) {
-    if (now > entry.resetTime) {
-      rateLimitStore.delete(key)
-    }
-  }
-}
-
 /**
  * Validate content length
  */