Per feedback, the model · permission-mode · context line reads better in
the status bar than as a strip above the conversation. Adds a generic,
publisher-agnostic status-bar context slot: a pane publishes a short
string to the `statusbar.context` MessageBus channel and the bar shows
the latest. The active Claude sub-tab publishes (inactive panes stay
quiet, so no race); switching tabs swaps the slot to the focused pane.
Replaces the in-pane ClaudeStatusStrip with a formatStatusLine helper +
PaneContextStatusItem (the status-bar widget) and a StatusItemContribution.
ClaudeSessionHost passes `active` so only the visible sub-tab publishes.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>