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/rmcp-client/tests/resources.rs

@@ -36,7 +36,7 @@ fn init_params() -> InitializeRequestParams {
         client_info: Implementation {
             name: "codex-test".into(),
             version: "0.0.0-test".into(),
-            title: Some("Codex rmcp resource test".into()),
+            title: Some("LLMX rmcp resource test".into()),
             user_agent: None,
         },
         protocol_version: mcp_types::MCP_SCHEMA_VERSION.to_string(),
@@ -92,7 +92,7 @@ async fn rmcp_client_can_list_and_read_resources() -> anyhow::Result<()> {
                 ),
                 mime_type: Some("text/plain".to_string()),
                 name: "codex-memo".to_string(),
-                title: Some("Codex Memo".to_string()),
+                title: Some("LLMX Memo".to_string()),
                 uri_template: "memo://codex/{slug}".to_string(),
             }],
         }