Robot descriptions v2.18.1

Clearer repository folders and navigation

The model packages keep their existing locations and entry filenames. This
release reorganizes authoring material and generated results:

• docs/maintenance/: build, publishing and historical authoring notes.
• docs/releases/: versioned release notes.
• docs/kinematics/: the printable robot review booklet.
• reports/{appearance,dynamics,grippers,kinematics,packages,history}/:
  generated records grouped by topic, including the JSON formerly in tools/.
• reports/kinematics/review/: offline side-by-side model comparison.
• docs/images/robots/: robot galleries and wrist-mounting illustrations.

New folder READMEs explain where to start. The shortened repository map links
to those indexes, the current model-status page and a complete move list.

Generators and documentation links use the new destinations. Existing CLI
script paths, model/scene/URDF names, ROS launch commands and download filenames
are retained. Checked geometry and texture-cache payloads are preserved; only
their generator fingerprints are refreshed for report-path-only code changes.

Geometry, colors, kinematics, inertia, collision shapes, joint limits and
actuation settings are unchanged. User-confirmed limits and the other physical
accuracy checks remain separate work. ROS/MoveIt setup and hardware integration
remain deferred for the user; existing integration support is retained.

Models/data/docs remain CC BY 4.0; support code remains Apache-2.0. Older tags
and published release archives retain their original layout.