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/protocol/src/models.rs

@@ -151,7 +151,7 @@ fn local_image_error_placeholder(
 ) -> ContentItem {
     ContentItem::InputText {
         text: format!(
-            "Codex could not read the local image at `{}`: {}",
+            "LLMX could not read the local image at `{}`: {}",
             path.display(),
             error
         ),

llmx-rs/protocol/src/protocol.rs

@@ -1,4 +1,4 @@
-//! Defines the protocol for a Codex session between a client and an agent.
+//! Defines the protocol for an LLMX session between a client and an agent.
 //!
 //! Uses a SQ (Submission Queue) / EQ (Event Queue) pattern to asynchronously communicate
 //! between user and agent.
@@ -45,7 +45,7 @@ pub const USER_INSTRUCTIONS_OPEN_TAG: &str = "<user_instructions>";
 pub const USER_INSTRUCTIONS_CLOSE_TAG: &str = "</user_instructions>";
 pub const ENVIRONMENT_CONTEXT_OPEN_TAG: &str = "<environment_context>";
 pub const ENVIRONMENT_CONTEXT_CLOSE_TAG: &str = "</environment_context>";
-pub const USER_MESSAGE_BEGIN: &str = "## My request for Codex:";
+pub const USER_MESSAGE_BEGIN: &str = "## My request for LLMX:";
 
 /// Submission Queue Entry - requests from user
 #[derive(Debug, Clone, Deserialize, Serialize, JsonSchema)]