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/view_image.rs

@@ -382,7 +382,7 @@ async fn view_image_tool_placeholder_for_non_image_files() -> anyhow::Result<()>
             content.iter().find_map(|span| {
                 if span.get("type").and_then(Value::as_str) == Some("input_text") {
                     let text = span.get("text").and_then(Value::as_str)?;
-                    if text.contains("Codex could not read the local image at")
+                    if text.contains("LLMX could not read the local image at")
                         && text.contains("unsupported MIME type `application/json`")
                     {
                         return Some(text.to_string());