Make the fleet dashboard usable on a phone (touch zoom, narrow layout)

[MJohnson459]

Make the fleet dashboard usable one-handed on a phone.

M3's network path was already verified from a phone on cellular
(m3-verification.md §6); the layout was still a desk's — three columns
collapsing to three stacked panes, so a 390 px screen got a map canvas a
couple of hundred pixels tall with the roster above it and the detail pane
below the fold.

What changed

• One pane at a time below 760 px, behind a tab bar at the bottom of the
  screen (thumb reach), so the map gets the whole display. Between 760 and
  1100 px the panes stack and scroll as before; the desktop layout is
  untouched.
• Picking a robot in the roster navigates to the map — what the desktop
  layout gets for free by showing both panes. The third tab is labelled with
  the selected robot's id, so the selection is legible without switching.
• Pinch to zoom, since there is no wheel: one finger pans, two zoom about
  the point between them, a two-finger drag carries the map along. Robot
  markers get a 24 px hit target under a coarse pointer instead of 14 px.
• A zone picker beside the dispatch box listing the floor's taught zones.
  It writes goto <zone> into the same box rather than sending it, so the
  grammar stays the robot's and no second command language appears in the
  server — it just removes the keyboard from the common case.
• Phone-specific fixes: 100dvh, env(safe-area-inset-bottom) under the tab
  bar, 16 px inputs (Safari zooms the page on a smaller one and never zooms
  back), touch-action: none on the canvas, finger-sized controls under
  pointer: coarse, and a header/toolbar that wraps instead of hiding the
  map's follow and fit off the right edge.

The breakpoint is a silent seam — CSS decides what is displayed, JS decides
when a selection navigates, and disagreement gives a tab bar over stacked
panes rather than an error — so it lives in the new server/ui/layout.mjs and
ui_test.mjs reads the stylesheet and holds it there. The pinch arithmetic
(pinchSpan/pinchUpdate) is pure and tested for the reason the Q5 transform
is: a division by a zero span puts NaN in the view scale and blanks the map
for good.

Three pre-existing bugs this found, all hidden by a desk

• hidden did not hide. .revisions and .dispatch set display: flex,
  which outranks the attribute's UA-stylesheet display: none — the promote
  picker rendered empty on every floor with no candidate.
• The canvas backing store was resized on width alone, so a height change
  (tab switch, toolbar rewrap, mobile URL bar) left clearRect unable to
  reach the bottom of it and the previous frame's scale bar stayed on screen
  under the new one.
• The scale bar was drawn in the dark theme's near-white over a basemap
  whose free space is white. A canvas gets no cascade, so it now reads
  --dim off the element and is legible in both themes.

How it was verified

Against a live stack (container broker on isolated ports, fleet server, three
scripted robots on the office_world bundle):

• ui_test.mjs 24/24 under node — the pinch maths, the CSS/JS breakpoint,
  every pane having a tab, touch-action: none.
• test_ui.py, test_fleet_server.py, test_map_registry.py — 64 passed.
• browser_check.mjs grew a phone pass (390x844, dpr 3, mobile metrics,
  touch emulation, real Input.dispatchTouchEvent): coarse pointer, one pane
  • tab bar, no sideways scroll on any pane, backing store follows the pane,
    roster tap lands on the map, two fingers zoom. 14/15 — the one failure
    is "the robot answered on task/status", expected here because the scripted
    robots publish state but run no task server.
• In a touch-enabled Playwright context: a tap 20 px off a marker selected
  it (inside the touch target, outside the mouse one), and after a pinch
  centred on that marker a tap at the same screen point still selected it —
  which is what shows the zoom anchors where the fingers are. A goto dropoff
  chosen from the picker dispatched through the API and wrote the expected
  audit row. Desktop at 1600x900 re-checked in both colour schemes.

Docs: docs/fleet/README.md §9 gained an "On a phone" section and a triptych
screenshot; measurements and the three bugs are m3-verification.md §9;
CLAUDE.md's M3 paragraph and mote_fleet/README.md's file table updated.

A real device is still the acceptance — emulation gets the viewport and
the touch points right and the thumb wrong. iOS Safari's 100dvh, the safe
area, the input-zoom rule and the on-screen keyboard are confirmed only in
Chrome. Filed as task #309.

Branch fleet-dashboard-phone, commit d300a8d. Not pushed.