v2.7.0-Plover

Refactor TSP: waypoint-only optimization, cached Dijkstra paths (v2.7.0)

The previous algorithm mixed waypoints and boundary helper vertices in the
same route list, so 2-opt was optimizing the wrong thing - it shuffled
visibility-graph helpers while leaving waypoint crossings unfixed.

Now find_tsp_route builds a waypoint-to-waypoint distance matrix using
Dijkstra on the visibility graph, caching every path. Nearest-neighbour
and 2-opt operate purely on the waypoint matrix. create_route_layer
stitches the final geometry from the cached paths. The old second-pass
boundary-correction code is removed - it was a workaround for the broken
first pass.