Daxia [ T3 Code ] Add terminal clipboard shortcuts

[daxia778]

/claim #824

Summary:

• Added platform-aware terminal clipboard shortcut helpers for Cmd+C / Cmd+V on macOS and Ctrl+Shift+C / Ctrl+Shift+V on Windows and Linux.
• Wired the xterm custom key handler so copy only fires when terminal text is selected, preserving no-selection Ctrl+C pass-through.
• Paste sends clipboard text through the existing terminal input path, and successful copy shows a brief toast.
• Added focused tests plus safe public metadata.

Demo:

• https://github.com/daxia778/Bounty-Hunters/releases/download/issue-824-demo-0eb7c517/t3-terminal-824-demo-0eb7c517.mp4

Validation:

• npx -y bun@1.3.11 run --cwd apps/web test src/keybindings.test.ts
• npx -y bun@1.3.11 run --cwd apps/web typecheck
• npx -y bun@1.3.11 run fmt:check apps/web/src/keybindings.ts apps/web/src/keybindings.test.ts apps/web/src/components/ThreadTerminalDrawer.tsx apps/web/src/components/_generation.json
• git diff --check

[github-actions]

Unfortunately the changes in this PR didn't fully resolve the issue. Please rework your solution and submit a new pull request.

Make sure to review the acceptance criteria in the linked issue and verify all conditions are met before resubmitting. See CONTRIBUTING.md for guidelines.