Add zone visualisation for GoToZone feature

[chart-singapore]

New feature implementation

Implemented feature

This is part of an 8-repo Simple GoToZone feature. Tracked in Stage A of open-rmf/rmf#726.

Extends NavGraphVisualizer so that zones published in the nav-graph message are rendered in RViz: a semi-transparent bounding box per zone, a floating name label, distinct markers for internal vertices, and a thinner line style for transition lanes.

Implementation description

NavGraphVisualizer

Parses the zones field and emits four distinct marker categories:

• Zone bounding box — semi-transparent CUBE marker per zone (sized by the zone's length/width and oriented by yaw), grouped by building level for independent visibility toggling.
• Zone name label — floating TEXT_VIEW_FACING marker anchored above each zone.
• Zone internal vertices — separate SPHERE_LIST marker in the zone_waypoints/ namespace, rendered smaller than regular waypoints so they stand out.
• Zone transition lanes — rendered with a reduced line width so they visually recede compared to normal graph lanes.

GenAI Use

We follow OSRA's policy on GenAI tools

• I used a GenAI tool in this PR.
• I did not use GenAI