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-cli/scripts/build_npm_package.py

@@ -28,7 +28,7 @@ COMPONENT_DEST_DIR: dict[str, str] = {
 
 
 def parse_args() -> argparse.Namespace:
-    parser = argparse.ArgumentParser(description="Build or stage the Codex CLI npm package.")
+    parser = argparse.ArgumentParser(description="Build or stage the LLMX CLI npm package.")
     parser.add_argument(
         "--package",
         choices=("llmx", "llmx-responses-api-proxy", "llmx-sdk"),