Browse previously submitted prompts using Up/Down arrow keys, similar to
shell history and Claude Code's prompt history feature.
- Up arrow when editor is empty: browse to older prompts
- Down arrow when browsing: return to newer prompts or clear editor
- Cursor movement within multi-line history entries supported
- History is session-scoped, stores up to 100 entries
- Consecutive duplicates are not added to history
Includes 15 new tests for history navigation behavior.
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