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-protocol/src/bin/export.rs

@@ -4,7 +4,7 @@ use std::path::PathBuf;
 
 #[derive(Parser, Debug)]
 #[command(
-    about = "Generate TypeScript bindings and JSON Schemas for the Codex app-server protocol"
+    about = "Generate TypeScript bindings and JSON Schemas for the LLMX app-server protocol"
 )]
 struct Args {
     /// Output directory where generated files will be written