[UX] Ctrl+C should not exit OpenCode - conflicts with universal copy shortcut

[SYRS-AI]

Description

Pressing Ctrl+C in OpenCode immediately exits the application. This is extremely frustrating because Ctrl+C is the universal copy shortcut on Windows (and commonly used on Linux too).

Users frequently press Ctrl+C out of habit when trying to copy text, and accidentally terminate their entire session - losing context and conversation history.

The Problem

Shortcut	User Expectation	OpenCode Behavior
Ctrl+C	Copy selected text	Exits application

This happens constantly during normal usage:

• Copying error messages to search online
• Copying code snippets from AI responses
• Copying file paths or commands
• General muscle memory from every other application

Expected Behavior

Option 1 (Recommended): Require double Ctrl+C or Ctrl+C twice within 1-2 seconds to exit

• First Ctrl+C: Show message "Press Ctrl+C again to exit"
• Second Ctrl+C: Actually exit

Option 2: Use a different exit shortcut

• Ctrl+D (common in Unix terminals for EOF/exit)
• Ctrl+Q (quit)
• /exit or /quit command only

Option 3: Make Ctrl+C cancel current operation only (like Claude Code)

• If AI is generating: Cancel generation
• If idle: Do nothing or show exit hint
• Never exit immediately on single Ctrl+C

Comparison with Other Tools

Tool	Ctrl+C Behavior
Claude Code	Cancels current operation, does NOT exit
Cursor	Copy (normal IDE behavior)
VS Code	Copy
Most CLI tools	Interrupt current command, not exit shell

Environment

• OS: Windows 11 (also affects Linux users)
• Terminal: Windows Terminal, PowerShell, Git Bash

Related Issues

• #7309 (mentions this issue but bundled with other requests)
• #7074 (CTRL_C_EVENT handling)

This deserves a dedicated issue due to its significant impact on user experience. Accidental exits cause real productivity loss.