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/process-hardening/src/lib.rs

@@ -38,7 +38,7 @@ pub(crate) fn pre_main_hardening_linux() {
     // For "defense in depth," set the core file size limit to 0.
     set_core_file_size_limit_to_zero();
 
-    // Official Codex releases are MUSL-linked, which means that variables such
+    // Official LLMX releases are MUSL-linked, which means that variables such
     // as LD_PRELOAD are ignored anyway, but just to be sure, clear them here.
     let ld_keys: Vec<String> = std::env::vars()
         .filter_map(|(key, _)| {