* Route new-tab link clicks to Orca tabs instead of popup windows
- Adds an isolated-world click/auxclick listener that relabels
browser-native new-tab intents (target=_blank, cmd/ctrl-click,
middle-click) with a private frame name, so setWindowOpenHandler can
distinguish them from opener-dependent window.open() calls without
breaking OAuth popups.
- Wires matched clicks through to a new browser:open-link-in-orca-tab
IPC payload carrying foreground/background activation intent, so the
renderer opens a worktree tab instead of a native window.
- Adds unit and e2e coverage for modifier/middle-click routing,
cancellation/rewrite handling, and cleanup on guest teardown.
* Route new-tab link clicks to Orca tabs and stop background popups
Plain target=_blank clicks (main frame and iframes) now navigate the
current Orca tab in place instead of opening a new browsing context,
while explicit new-tab gestures (Cmd/Ctrl-click, middle-click,
Shift+modifier) route into Orca tabs via one-use private frame names,
including child frames. Drops the foreground/background frame-name
split and the activate flag now that all routed links always open
active — no more silent background popups from a plain link click.
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