Release 0.18.2: scroll chat history at an empty prompt

[mostlydev]

Restores conversation scrolling after 0.18.1 turned off mouse capture.

Summary

• With the suggestion list closed and an empty draft, Up/Down scroll the conversation. This also covers wheel gestures that terminals translate into arrow keys once mouse capture is off.
• Ctrl+P / Ctrl+N recall submitted prompts. Non-empty drafts, multi-line editing, and the suggestion list keep their existing controls.
• Help and README updated.

Includes chat-empty-draft-scroll rebased onto the 0.18.1 merge, with the changelog entry moved back under Unreleased.

Verification

• npm run typecheck, npm test (573 passed, 1 skipped), npm run build, git diff --check
• Live: three Up presses scroll the conversation, leave the draft empty, and show the scrolled hint.