[ENHANCEMENT] Ctrl+R history search should be case-insensitive

Feature Request

The reverse search (Ctrl+R) for command history is currently case-sensitive, which makes it harder to find previous inputs.

Expected Behavior

Ctrl+R search should be case-insensitive by default, matching the behavior of most shell implementations (bash, zsh, fzf).

Current Behavior

Searching for "test" won't match history entries containing "Test" or "TEST".

Rationale

• Standard shell reverse-search is typically case-insensitive
• Users rarely remember the exact casing of previous inputs
• Case-insensitive search is more forgiving and user-friendly