SU.1112 Live in every app: see each other's cursors and names while co-editing

Asked (#1112, Oct 28): collaboration where people see each other's cursors, so working in teams is easier.

CadCraft's Live already shows other people's cursors and selections (live.js presence). Do: the same presence layer in the other apps' Live sessions (cursor, name colour, selection), reusing the CadCraft code through the shared Live library. Relates to DC.27 and EG.41.

**Implementation started 2026-11-02** (0.9 pick #7, second five, hardest first; session `live-cursors-09`, log docs/0.9-sessions/live-cursors-09.md). Status moves to Partly built or Built only when the code is reachable and tested (rule 49).

**Built 2026-11-02** (session `live-cursors-09`, log docs/0.9-sessions/live-cursors-09.md): one shared presence layer (assets/js/live-presence.js, synced by tools/shell/sync.mjs) with a thin adapter in each app's live.js; BimCraft, ModelCraft, TakeoffCraft, CivilCraft, DetailCraft and PartCraft now show cursors, names in the person's color and selections; CadCraft and MarkupCraft keep their own views on the same palette. Tested with two real pages per app (tools/live-apps-test/browser-apps.mjs) and test-presence.mjs.