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/app-server/tests/suite/v2/turn_start.rs

@@ -31,7 +31,7 @@ const DEFAULT_READ_TIMEOUT: std::time::Duration = std::time::Duration::from_secs
 #[tokio::test]
 async fn turn_start_emits_notifications_and_accepts_model_override() -> Result<()> {
     // Provide a mock server and config so model wiring is valid.
-    // Three Codex turns hit the mock model (session start + two turn/start calls).
+    // Three LLMX turns hit the mock model (session start + two turn/start calls).
     let responses = vec![
         create_final_assistant_message_sse_response("Done")?,
         create_final_assistant_message_sse_response("Done")?,
@@ -131,7 +131,7 @@ async fn turn_start_emits_notifications_and_accepts_model_override() -> Result<(
 
 #[tokio::test]
 async fn turn_start_accepts_local_image_input() -> Result<()> {
-    // Two Codex turns hit the mock model (session start + turn/start).
+    // Two LLMX turns hit the mock model (session start + turn/start).
     let responses = vec![
         create_final_assistant_message_sse_response("Done")?,
         create_final_assistant_message_sse_response("Done")?,