feat: show the session's lich errands in the prompt footer

[omartelo]

Client side of lich's mod-status contract (lichdotdev/lich#663, not merged yet). Every 5 seconds an interactive session inside lich reads GET /mod/status and shows its errands in the status line, for example lich: owes "docs" an answer, 2 tasks out (1 waiting), 1 answer to collect. Reading never collects. A 404 (a lich older than the contract) stops the reads.

• The fixture is pinned at lich 6c207ba in refresh-fixtures.sh until a lich release ships it.
• Every worker agent-cards opens is an errand of this session, so while the errands show, the worker count is left out of the line (hooks/status-line.js).
• tests/mod-control.engine.test.ts: the fake lich answers /mod/status the way the real one does (no errands) and stands for ui.status. Before this, the new read was consuming the command batches. No assertion changed.

Tests: node --test tests/*.test.mjs 325 pass, claude plugin test . 27 pass, claude plugin validate passes.

Update: the whole lich line (errands, worker count, edit-guard note) moved off $.ui.status, which Claude Code draws as a yellow ⚠ warning under the prompt. It is now drawn dim among the mode labels at the right of the footer, by a ui.render hook on SessionMode in hooks/status-line.js. Mods set their part and call $.ui.invalidate("ui.render"). Tests: 326 node, 27 engine.