cmux copy selection does not sync to local clipboard

Problem

Copy selection with auto-copy in Jcode does not work correctly when running through cmux/browser-backed terminals.

Observed behavior:

• Drag/select text in the Jcode TUI.
• Jcode reports that the selection was copied.
• The browser/local clipboard is not updated, so paste does not contain the selected text.

Likely cause

The existing clipboard path uses host-side clipboard integrations such as wl-copy and arboard. In a remote or browser-backed terminal environment, these can succeed while only updating the remote host clipboard, not the user's local/browser clipboard.

Proposed fix

Emit an OSC 52 clipboard escape sequence whenever Jcode copies selected text, while preserving the existing host clipboard behavior. OSC 52 lets terminal frontends synchronize copied text to the user's local clipboard when supported.

PR

Proposed fix: https://github.com/1jehuang/jcode/pull/332

Validation in PR

• cargo fmt
• cargo test clipboard_tests::osc52_clipboard_sequence --lib
• cargo test test_copy_selection_mouse_drag_auto_copies_and_exits_mode --lib

Start with proposed PR #332 and the clipboard-related code it changes. Run the listed OSC 52 and mouse-drag clipboard tests; the issue is complete when those tests pass and the local clipboard synchronization behavior is covered without regressing existing host clipboard behavior.