Adds the Layer 4 observability view to the control pane: a self-contained,
dependency-free 3D point-cloud of the agent airspace (positions from the
proximity embedding, sized by working set, colored by collision risk, links
for converging pairs) plus an XSS-safe advisory panel that polls every 5s.
- proximity-viz.js: renderProximityVizHtml() (canvas projection, no external JS)
- server.js: GET /proximity (page) + GET /api/proximity (snapshot.proximity feed)
- test: asserts both routes serve and the feed carries positions/links/advisories
