Reorganize auth implementation to /src/auth/ for better organization (#130)

- Move real JWT implementation from src/c_api/mcp_c_auth_api.cc to src/auth/mcp_auth_implementation.cc
- Remove old stub files (auth_c_api.cc, http_client.cc, jwks_client.cc)
- Update CMakeLists.txt to reference the new auth implementation location
- Disable test files for removed stubs to fix linker errors
- Keep all JWT validation, JWKS fetching, RSA verification functionality intact

Author: RahulHere

CMakeLists.txt

@@ -347,9 +347,8 @@ message(STATUS "")
 
 # Source files - split core from client/server to avoid circular deps
 set(MCP_CORE_SOURCES
-    src/auth/http_client.cc
-    src/auth/jwks_client.cc
-    src/auth/auth_c_api.cc
+    # Auth implementation is now in src/auth/mcp_auth_implementation.cc
+    # and is included via src/c_api/CMakeLists.txt in the gopher_mcp_c library
     src/buffer/buffer_impl.cc
     src/json/json_bridge.cc
     src/json/json_serialization.cc