tab-bridge.js (moved from wayBetter for X) is served by bridge::SOURCE,
or by bridge::script(BridgeOptions) with shortcut and link-drag
forwarding switched off for a shell that does not handle them (a
forwarded shortcut is taken from the page). Tests: one options line,
only tab_report/tab_shortcut/tab_link_drag, every forwarded shortcut is
one tabs::valid_shortcut accepts. Generated apps now inject
bridge::script(BridgeOptions::REPORT_ONLY) instead of writing their own
duplicated src-tauri/runtime/tab-bridge.js.