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/src/rollout/policy.rs

@@ -8,7 +8,7 @@ pub(crate) fn is_persisted_response_item(item: &RolloutItem) -> bool {
     match item {
         RolloutItem::ResponseItem(item) => should_persist_response_item(item),
         RolloutItem::EventMsg(ev) => should_persist_event_msg(ev),
-        // Persist Codex executive markers so we can analyze flows (e.g., compaction, API turns).
+        // Persist LLMX executive markers so we can analyze flows (e.g., compaction, API turns).
         RolloutItem::Compacted(_) | RolloutItem::TurnContext(_) | RolloutItem::SessionMeta(_) => {
             true
         }