Support mouse click to position cursor in input area

Feature Request

Is your feature request related to a problem?
When using Claude Code in iTerm2 (and likely other terminal emulators that support mouse reporting), there's no way to click within the text input area to position the cursor. In a normal terminal prompt, iTerm2 supports Option+Click to move the cursor to the clicked position, but this doesn't work inside Claude Code's TUI.

Describe the solution you'd like
Support mouse click (or Option+Click) to position the cursor within the Claude Code input area. Most modern terminal emulators support mouse event reporting, so Claude Code could listen for these events and move the cursor accordingly.

Describe alternatives you've considered

• Keyboard navigation (Ctrl+A/E, Ctrl+Left/Right, arrow keys) works but is slower for long inputs
• Vim mode keybindings help but have a learning curve

Additional context
iTerm2 and many other terminal emulators already support mouse position reporting. This would be a natural UX improvement for users accustomed to clicking to position their cursor.