Add scene clock with assistant-controlled updates

[rwilkin]

Summary

Adds an optional per-chat Scene Clock for roleplay conversations.

• Adds manual date, time, format, calendar, and notes controls to the chat menu.
• Injects the current Scene Clock state into generation prompts, including existing saved prompt orders and custom templates.
• Persists Scene Clock settings through the chat update API.
• Optionally allows assistants to update the clock using hidden structured markup.
• Removes valid assistant update markup from visible chat messages and safely ignores malformed updates.

Why

Roleplay conversations often need a persistent in-scene date and time that is independent of real-world time. Keeping this state in the chat and prompt prevents the model from losing track of time across longer conversations.

Validation

• npm.cmd run typecheck
• npm.cmd run build:server
• npm.cmd run build:win
• npm.cmd test — 75 passing