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/core/tests/suite/review.rs

@@ -40,7 +40,7 @@ use wiremock::matchers::path;
 /// in that order when the model returns a structured review JSON payload.
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn review_op_emits_lifecycle_and_review_output() {
-    // Skip under Codex sandbox network restrictions.
+    // Skip under LLMX sandbox network restrictions.
     skip_if_no_network!();
 
     // Start mock Responses API server. Return a single assistant message whose