Minor fixes to Octopus, Chat and Whatif

What's Changed

• fix: add yaml language tag to Hanchu iESS bridge script code block by @upton68 in #4836
• fix: mask the Octopus API key on the What If tab as a password field by @springfall2008 in #4838
• Accept Octopus free-session events with code: null by @chalfontchubby in #4837
• fix(chat): keep the model picker on-screen and make set_config type-safe by @springfall2008 in #4839

Full Changelog: v8.54.0...v8.54.1