Terminal select-to-copy

Motivation

Selecting text with the mouse in the browser terminal did not place the selection on the clipboard. Users had to right-click (PuTTY-style copy) or use a keyboard shortcut, which was non-obvious and broke the muscle memory of a normal Linux terminal.

User-facing change

• Dragging a mouse selection in the ElasticBLAST Terminal now copies the highlighted text to the system clipboard as soon as the selection settles (Linux/PuTTY "select-to-copy" behaviour).
• The existing right-click copy/paste behaviour is unchanged.

Implementation

• web/src/pages/RemoteTerminal.tsx: added a mouseup listener on the xterm container (handleTerminalMouseUp) that reads term.getSelection() and writes it to navigator.clipboard. The listener is registered alongside the existing capture-phase contextmenu handler and torn down in the same effect cleanup.
• Clipboard writes are best-effort: failures in an insecure context are ignored, matching the existing right-click copy path.

Validation

• cd web && npm run build — passes.
• npx vitest run src/pages/remoteTerminalProtocol.test.ts — 4 passed.