Routes: movers along waypoints (roadmap 8)

New route prefab (routes.rhai): cars, buses, motorbikes, cyclists, people,
deer or elephants move along waypoints, round a loop or there and back.
Each way keeps to the left of the line (or right), corners are rounded
into pieces of at most 45 degrees; there-and-back routes become loops with
U-turns, so the two directions never share a strip.

Engine: Prim::Travel / sprite.begin_travel / script travel(a, b, dur,
windows) ... end(): the mover is drawn at a piece's start and slides to
its end while it is on that piece, hidden otherwise. The renderer writes
keyframes per piece (named by a hash of their content) into one <style>
per view. Each piece is its own sprite with the lane strip as its sort
extent (ext_reset), mitred at the corners, so movers pass in front of and
behind trees, lamps and houses. Movers that look alike and never meet on
a piece share one drawing. iso-travel pauses (not hides) in still,
reduced-motion and ghosted views.

Studio: meta shape "path" draws point by point (snapping like runs) and
saves one object with pts; ending on the first point closes the loop.
MCP: pts in the object schema, route guidance.

Demos: streets gets traffic round the block, a bus, motorbikes, cyclists
and strolling people (replacing the one-axis cars); country gets cars on
the lane.

Tests: Rust 79 (each mover on exactly one piece at every moment, in every
rotation), Studio 125, web 99.

crates/isokit-theme/themes/default.toml

@@ -272,6 +272,8 @@ mach3 = "#5b6370"
 mach4 = "#b8692b"
 robot = "#e07a1f"
 robotb = "#3a3f48"
+# route paths
+route = "#e0b84a"
 # wildlife and garden
 deer = "#8a5a32"
 deerl = "#d6c4a6"
@@ -581,6 +583,7 @@ mach3 = "#8a93a1"
 mach4 = "#e08a43"
 robot = "#f08c2b"
 robotb = "#5a616d"
+route = "#b0802a"
 deer = "#a8703f"
 deerl = "#ecdfc8"
 nose = "#3a302a"
@@ -918,6 +921,7 @@ f-conc = "conc"
 ".iso-svg .iso-win" = "fill: var(--iso-win); stroke: none"
 ".iso-svg .iso-school" = "pointer-events: none"
 ".iso-svg .iso-swimbox" = "fill: none; stroke: none"
+".iso-svg .iso-route" = "fill: none; stroke: var(--iso-route); stroke-width: 1.2; stroke-dasharray: 5 4; stroke-linecap: round; stroke-linejoin: round; opacity: .75"
 ".iso-svg .iso-antler" = "fill: none; stroke: var(--iso-antler); stroke-width: .35; stroke-linecap: round; stroke-linejoin: round"
 ".iso-svg .iso-bristle" = "fill: none; stroke: var(--iso-bristle); stroke-width: .5; stroke-linecap: round"
 ".iso-svg .iso-bird, .iso-svg .iso-wing" = "stroke: none"