Feature request: word autocomplete in prompt input

When typing in the CLI prompt, tab-completing dictionary words would reduce
typos and speed up conversational input. This is distinct from the existing
command/path completion — it would target natural language words in the prompt
text itself.

Proposed behavior:

• Tab completes the current word against a dictionary
• Does not trigger on strings that look like code, paths, or commands
• Consistent with how some shells handle spell/word completion

This would be most useful in sessions that mix conversational direction with
coding tasks, where the user is frequently switching between natural language
and technical input in the same prompt.