Plans a grid of up to nine live sessions side by side. All tiles are
equal TerminalTiles, the main terminal is parked while the grid is
open, and activeSessionId follows the focused tile. The split pane stays
and shares the tile class. PR 1 builds the seams and TerminalTile, so
the split's second pane gains reconnect, exactly-once input, links,
image paste and focus-following shortcuts. PR 2 adds the grid.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
