🧹 chore: Remove Unused Cache Configuration Keys (#9551)

* Remove unused STATIC_CONFIG and LIBRECHAT_YAML_CONFIG cache keys.

These cache keys were identified as dead code - they were being written to but never read from anywhere in the codebase after a recent refactor:

- STATIC_CONFIG was used as a cache namespace that stored configuration data
- LIBRECHAT_YAML_CONFIG was the key used within that namespace to store parsed YAML config
- The cache.set() operation in loadCustomConfig.js stored the config but no cache.get() operations retrieved it
- Configuration data is already handled through other mechanisms without caching

* # removed tests regarding cache

api/cache/cacheConfig.spec.js

@@ -157,12 +157,11 @@ describe('cacheConfig', () => {
 
   describe('FORCED_IN_MEMORY_CACHE_NAMESPACES validation', () => {
     test('should parse comma-separated cache keys correctly', () => {
-      process.env.FORCED_IN_MEMORY_CACHE_NAMESPACES = ' ROLES, STATIC_CONFIG ,MESSAGES ';
+      process.env.FORCED_IN_MEMORY_CACHE_NAMESPACES = ' ROLES, MESSAGES ';
 
       const { cacheConfig } = require('./cacheConfig');
       expect(cacheConfig.FORCED_IN_MEMORY_CACHE_NAMESPACES).toEqual([
         'ROLES',
-        'STATIC_CONFIG',
         'MESSAGES',
       ]);
     });