Enable Sign out during initial FullPage capture

[wikirby]

Summary

On opening the clipper, Sign out was disabled while the initial full-page capture ran, and only re-enabled once that capture completed. Since mode buttons stay interactive during capture (added in "Allow mode switching during initial FullPage capture"), a user could switch to Article/Selection/Bookmark/Region before the capture finished — and in those modes Sign out was never re-enabled, leaving it stuck disabled.

Root cause

disableSignout() fired on dialog open and in switchToFullPage(). Sign out was only re-enabled by capture completion (finalize), PDF mode, or the no-capture invoke path — none of which run when the user pivots to another mode mid-capture.

Fix

• Remove the capture-time disableSignout() calls. Sign out now locks only during the save round-trip, via lockSidebar() / unlockSidebar().
• Remove the now-redundant standalone enableSignout() calls (PDF mode, no-capture ready state, finalize, sign-out reset), so Sign out state is driven entirely by lock/unlock.
• Abort any in-flight capture when the user signs out, so the worker's capture loop doesn't outlive the session.

Net invariant: Sign out state == save-lock state, always.

Testing

• npm run build clean (compile + lint)
• Open clipper, switch modes mid-capture -> Sign out stays available
• Save round-trip -> Sign out disabled during save, re-enabled after
• Sign out mid-capture -> capture aborts cleanly, returns to sign-in panel

[aanchalbhansali]

Approved