Complete comprehensive Codex → LLMX branding update

Fixed all remaining user-facing "Codex" references across entire codebase:
- Updated all UI strings and error messages
- Fixed GitHub issue templates and workflows
- Updated MCP server tool descriptions and error messages
- Fixed all test messages and comments
- Updated documentation comments
- Changed auth keyring service name to "LLMX Auth"

Reduced from 201 occurrences to only code identifiers (struct/type names).
Changes span 78 files across Rust, Python, YAML, and JSON.

🤖 Generated with Claude Code

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

llmx-rs/core/tests/suite/compact.rs

@@ -122,7 +122,7 @@ async fn summarize_context_three_requests_and_instructions() {
     };
     let third_request_mock = mount_sse_once_match(&server, third_matcher, sse3).await;
 
-    // Build config pointing to the mock server and spawn Codex.
+    // Build config pointing to the mock server and spawn LLMX.
     let model_provider = ModelProviderInfo {
         base_url: Some(format!("{}/v1", server.uri())),
         ..built_in_model_providers()["openai"].clone()
@@ -257,7 +257,7 @@ async fn summarize_context_three_requests_and_instructions() {
         "third request should not include the summarize trigger"
     );
 
-    // Shut down Codex to flush rollout entries before inspecting the file.
+    // Shut down LLMX to flush rollout entries before inspecting the file.
     codex.submit(Op::Shutdown).await.unwrap();
     wait_for_event(&codex, |ev| matches!(ev, EventMsg::ShutdownComplete)).await;