feat(agent): copy review prompt directly

[kerim1510]

Motivation

As a happy Hunk user, I copy the agent prompt every now and then. Opening a dialog just to copy it felt unnecessarily cumbersome, so this PR makes the menu action copy the prompt directly.

Less is more.

Summary

• replace the Agent skill dialog with a direct Copy agent prompt menu action
• expose the action as the unbound hunk.app.copyAgentPrompt command
• hide and disable the action when OSC 52 clipboard support is unavailable
• move the canonical agent prompt beside the Hunk review skill surface
• remove the obsolete modal state, rendering, lazy import, and Escape handling
• update keybinding documentation and release notes

Testing

• bun run typecheck
• bun run lint
• targeted AppHost, command, and menu tests (92 passed)
• bun run test:integration (64 passed)
• real TTY smoke run against the working-tree diff

The full unit and transcript-smoke runs were attempted, but this sandbox prevents
loopback socket binding and some smoke subprocess startup. The feature-specific
tests and the complete PTY integration suite pass.

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