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/feedback/src/lib.rs

@@ -214,7 +214,7 @@ impl CodexLogSnapshot {
 
         let mut envelope = Envelope::new();
         let title = format!(
-            "[{}]: Codex session {}",
+            "[{}]: LLMX session {}",
             display_classification(classification),
             self.thread_id
         );