Add copy/paste for selected states

[JustABiologist]

Summary: Adds Ctrl/Cmd+C to copy selected automaton states. Adds Ctrl/Cmd+V to paste fresh states offset from the copied selection while preserving state labels, accepting status, and transitions whose endpoints are in the copied selection. Leaves normal browser copy/paste alone while editing state and transition inputs. Verification: node -c site/js/editor.js; node-based smoke test for copying and pasting a two-state selection and its transition. Closes #37. If accepted for the listed bounty, PayPal payout can be sent to stab.me.papi@gmail.com.

[JustABiologist]

Manual test matrix for the copy/paste bounty:

• Select two states and copy with Ctrl+C.
• Paste with Ctrl+V and confirm new states are created with distinct ids.
• Confirm the pasted states preserve topology, including the internal transition between copied states.
• Confirm transitions to states outside the selection are not copied as dangling edges.
• Syntax check passed for site/js/editor.js; I also ran a Node smoke test over the copy/paste helper path.