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/interrupt.rs

@@ -49,7 +49,7 @@ async fn shell_command_interruption() -> anyhow::Result<()> {
     let shell_command = vec!["sleep".to_string(), "10".to_string()];
 
     let tmp = TempDir::new()?;
-    // Temporary Codex home with config pointing at the mock server.
+    // Temporary LLMX home with config pointing at the mock server.
     let codex_home = tmp.path().join("codex_home");
     std::fs::create_dir(&codex_home)?;
     let working_directory = tmp.path().join("workdir");