cleanup(path-inspector): remove unreachable showOnMap branch that calls undefined window.drawPacketRoute #143

Summary

Low-priority cleanup. public/path-inspector.js showOnMap() has an "already on #/map" branch that calls window.drawPacketRoute, but public/map.js only exposes window.drawPacketRouteMulti (around line 1368), not window.drawPacketRoute. If that branch ever ran, "Show on map" would silently do nothing.

Not user-visible today (verified by reading master d264716c):

• The standalone Path Inspector lives at #/tools/path-inspector, so showOnMap() always takes the first branch: it stores window._pendingPathInspectorRoute and navigates to #/map, where map.js (around line 1732) draws it with its local drawPacketRoute. This works.
• The Path Inspector pane embedded in the map page (map.js, around line 2464) calls the local drawPacketRoute directly. This also works.
• The else branch in path-inspector.js (around lines 180–191) is therefore unreachable in normal navigation, and it hides a broken call.

Found by the issue-batch agent while working on #123; the user-visible impact it reported was checked and does not hold.

Proposed cleanup

Pick one and keep it small:

1. Remove the unreachable else branch (and its comment), leaving the pending-route + navigate path as the only behaviour; or
2. Expose window.drawPacketRoute = drawPacketRoute next to window.drawPacketRouteMulti in map.js, so the branch works if it ever becomes reachable.

Option 1 is preferred (less surface, no new global). If #123's PR already touches the Path Inspector wiring in map.js, this can be folded into it instead.

Acceptance criteria

• No code path calls an undefined window.drawPacketRoute.
• "Show on map" from #/tools/path-inspector and from the map's embedded pane still draws the route (existing tests or a small new one).
• No behaviour change elsewhere.