[FEATURE] Add modifier key requirement for copy-on-select (e.g., Shift+select)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Copy-on-select copies text to clipboard via OSC 52 on every mouse selection. Any accidental text selection overwrites your clipboard, and the "sent N chars via OSC 52" toast flashes constantly.

Proposed Solution

Add a setting to require a modifier key:
{ "copyOnSelect": "shift" | "always" | "disabled" }

• "always" ΓÇö current behavior
• "shift" ΓÇö only copies when Shift is held during selection
• "disabled" ΓÇö never auto-copy, use /copy instead

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

Interactive mode (TUI)

Use Case Example

_No response_

Additional Context

You're reading through a long Claude response, scrolling and occasionally selecting text to track your place. Each selection silently overwrites your clipboard. Later you Ctrl+V expecting to paste something you copied earlier from another app, and instead get a random fragment of Claude's output.