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/tui/src/bottom_pane/feedback_view.rs

@@ -422,7 +422,7 @@ pub(crate) fn feedback_upload_consent_params(
             super::SelectionItem {
                 name: "Yes".to_string(),
                 description: Some(
-                    "Share the current Codex session logs with the team for troubleshooting."
+                    "Share the current LLMX session logs with the team for troubleshooting."
                         .to_string(),
                 ),
                 actions: vec![yes_action],