[FEATURE] Add "Copy to clipboard" button for code blocks and command output

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

When selecting and copying text from Claude Code's terminal UI, extra whitespace and line breaks are inserted due to terminal soft-wrapping. This makes copying
code snippets, SQL queries, and multi-line commands unreliable — the pasted result needs manual cleanup every time.

Tools like Cursor provide a one-click "copy block" button next to code output that copies the raw content cleanly.

Just like you see broken tabs and spaces in the above problem statement

Proposed Solution

Option A: Keyboard shortcut to copy last code block

Add a keybinding (e.g., Ctrl+Shift+C or a custom chord) that copies the
most recent code block or command output to the system clipboard. Fast,
no mouse needed, fits the CLI-first workflow.

### Option B: Inline copy affordance in rendered output
Display a small [Copy] indicator next to each code block / command output
(similar to how Cursor, GitHub, and ChatGPT render copy buttons). Clicking
or pressing a key while focused copies the raw content without terminal
wrapping artifacts.

### Option C: Slash command — /copy
A /copy command that copies the last assistant code block (or Nth block
via /copy 2) to clipboard. Minimal UI change, works in all terminals.

### Any of the above should:

• Copy raw content, not terminal-rendered text (no soft-wrap line breaks)
• Preserve original indentation
• Work across macOS, Linux, and WSL
• Support both code blocks and shell command output

Alternative Solutions

Requested Feature

Add a clickable "copy to clipboard" affordance (button or keyboard shortcut) on:

• Code blocks in assistant responses
• Command output blocks
• Inline code snippets

This should copy the raw content without terminal wrapping artifacts.

## Workarounds Currently Used

• Piping output to pbcopy (works but requires asking the assistant explicitly)
• Writing to temp files and opening in an editor
• Using iTerm2/tmux copy mode (reduces but doesn't eliminate the issue)

## Environment

• macOS (Terminal.app / iTerm2)
• Claude Code CLI

Priority

High - Significant impact on productivity

Feature Category

CLI commands and flags

Use Case Example

You can see everything I have written above has broken tabs and spaces and line breaks.

Additional Context

_No response_