Consolidates duplicated logic behind shared implementations — paginated
grid tabs, focus chrome, cached remote stores, sheet selection columns,
the server artifact store and a test fixture layer — and removes code
that had become unreachable. Net reduction of about 5,500 lines with no
behaviour change.
Where a fix had landed separately in code that moved into a shared
helper, the fix was re-applied inside the helper rather than left behind
in the copy that went away.
Collapses indirection layers and one-caller abstractions across the video
player, shortcut dispatch, shader loading and context-menu code, including
the VideoPIPManager pass-through over PipService.
edde746