Add goto <zone> and optional zone footprints ("go to the kitchen")

[MJohnson459]

Adds place-based navigation — goto <zone> ("go to the kitchen") — to the task layer.

One concept: a "zone"

Review feedback on the first cut was that zones and regions were two names for the same thing — a named pose you navigate to — and that a zones.yaml holding both was confusing. So this collapses them into a single concept:

• A zone is a named pose the robot navigates to. fetch (its pickup/dropoff waypoints) and goto <zone> both resolve names against the one zones: table — goto kitchen, goto home, any zone works.
• A zone may carry an optional area footprint (a radius circle) that turns it into a room and answers "am I inside it?" (zones.containing()). The footprint is optional metadata on the single concept — not a second type — so there's one YAML section, one loader, one teach command.

frame_id: map
zones:
  pickup:  {x: 1.8, y: -1.5, yaw: 0.0}      # bare waypoint
  kitchen: {x: 2.0, y: 2.0, radius: 1.5}    # room: pose + circular footprint

The footprint is deliberately extensible: Zone.footprint is selected in one place (_footprint()), so a polygon: (explicit vertices, e.g. from map room-detection) slots into the same seam later — see follow-ups below.

Changes

• mote_tasks/zones.py — load_zones → {name: Zone(name, pose, footprint)}; Circle footprint with a clear seam for a future Polygon; containing() membership query (nearest-pose first); append_zone/save_zone gain an optional --radius.
• trees/goto.py + trees/common.py (shared WaitForTask + the task blackboard key). task_server hosts both the fetch and goto trees and dispatches on the command's first word (fetch/goto; unknown rejected), publishing accepted/succeeded/failed on task/status.
• Sites — zones (with optional footprints) live in the floor's zones.yaml, resolved via sites.py; site info shows N zones, M with a footprint.
• Sim worlds gain a few room zones (mote_world/office_world by hand; hospital_world via gen_hospital.py, regenerated — SDF byte-identical, single zone-clearance assertion). The default fallback zones.default.yaml mirrors mote_world so goto kitchen works out of the box.
• Docs — CLAUDE.md + mote_tasks/README.md rewritten around the single concept.

Testing

• pixi run lint, pixi run build, pixi run test (97 tests, 0 failures), pixi run sim-test — all green.
• New unit tests: test_goto_command (parser), test_goto_tree (full goto tick + dispatch against a mock navigate_to_pose), and test_zones extended to cover footprints and containing().
• Live headless sim on this code: goto kitchen drove the robot to the room and reported succeeded: goto kitchen on two worlds — office_world.sdf and mote_world.sdf.

Follow-ups (out of scope here)

• Polygon footprints beyond circles (#174).
• Auto-segment a saved map into room zones (#175).

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