fix: v0.10.2 drag-select stays highlighted and copies

A left drag in the pane is turned into xterm's own selection (as Shift+drag
does) instead of tmux copy-mode, which dropped the highlight on release.
Copy on release with a toast; Ctrl+C copies when something is selected.
Wheel scroll and status-line clicks still reach tmux. Closes #51

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WHRLCCdXYm41Qx5kNhehaP

README.md

@@ -71,7 +71,8 @@ The tmux server runs in its own unit, so every Claude process lives in **that**
 | Ctrl-b 0 / 1 | Claude window / shell window |
 | Ctrl-b s | Switch session (the URL follows) |
 | Ctrl-b d | Detach (the session keeps running) |
-| Shift+drag | Native browser selection (plain drag goes to tmux copy-mode, which copies via OSC 52) |
+| Drag | Selects text; it stays highlighted and is copied when you let go. Double-click selects a word, triple-click a line. Clicks on the tmux status line still go to tmux. |
+| Ctrl+C | Copies the selection when there is one; otherwise interrupts as usual |
 | Ctrl+Shift+C / V | Copy selection / paste |
 | Ctrl+Shift+P | Command palette (also the ⌕ button) |
 | Ctrl+Shift+E | Files pane (Esc: back, then close) |