Feature request: Case-insensitive reverse history search (Ctrl+R)

Feature Request

Ctrl+R reverse history search is case-sensitive with no option to make it case-insensitive.

Current behavior

Reverse history search (Ctrl+R) is case-sensitive only. Searching for "read" won't match a previous input of "Read PROMPT.md".

Desired behavior

Either:

1. Make reverse history search case-insensitive by default, or
2. Add a configuration option (e.g., historyCaseSensitive: false) to toggle case sensitivity

Why

Most shell reverse-search implementations (bash, zsh, fzf) are case-insensitive or offer a toggle. Case-insensitive search is more forgiving and generally more useful for recalling previous prompts.