feat(app): add --clipboard so Enter copies the drawing via OSC 52

[unclecode]

First of all, Thanks for publishing this under MIT - it is a genuinely nice tool.

Why

Exporting is currently the only way to get a drawing out of termDRAW. When the goal is simply to paste the art somewhere - a README, an issue, a chat with a coding agent - that means leaving the editor and dealing with a file. This adds an opt-in copy path so the drawing can go straight to the clipboard.

What

• @termdraw/opentui: new onCopy option alongside onSave. When a host wires it, Enter routes to copy and Ctrl+S keeps exporting. When it is omitted, Enter and Ctrl+S stay merged exactly as they are today. The footer renders whichever binding is active (Enter Copy • Ctrl+S Export Art vs. the current Enter/Ctrl+S Export Art).
• @termdraw/app: new --clipboard / -c flag, which wires onCopy to emit OSC 52.
• Copying leaves the editor open, unlike export — copying is not a way of finishing, so the drawing stays editable and can be copied again after further edits. The status bar confirms with Copied drawing to clipboard.

This is entirely opt-in. With no onCopy handler and no --clipboard flag, behavior is unchanged; there is a test asserting Enter still saves in that case.

Why OSC 52

OSC 52 is handled by the terminal rather than the host OS, so it works unchanged over SSH and inside multiplexers, where a local helper like pbcopy would only ever reach the remote machine.

Caveats, documented in the README:

• It is fire-and-forget. Terminals send no acknowledgement, so a terminal that does not implement OSC 52 (or has it disabled) ignores the request silently.
• tmux forwards it only when set-clipboard is on or external.
• screen needs its own wrapper; that is not handled here.

Validation

• bun run lint - clean
• bun run typecheck - clean across all three packages
• bun run build - passes
• bun test - 82 pass / 5 fail before, 87 pass / 5 fail after. The 5 remaining failures are pre-existing PTY timeouts in the tuistory-driven specs; they reproduce identically on an unmodified checkout in this environment.
• bun run format:check - could not run here: oxfmt resolves a config from a directory above the repo and fails on an unrelated file outside the checkout. Formatting was verified instead by running oxfmt against a clean git archive export of the tree, which reported all files correctly formatted.

Also verified by hand in a terminal: drawing, pressing Enter, and pasting the result elsewhere; Ctrl+S still exporting and exiting while --clipboard is active; and the footer text in both modes.

Cheers