Multi-select, select joined walls and fences, pond with swimming fish

Selection: S.sel stays the object picked last; S.selIds holds everything
selected.
- In the object list, Ctrl+click adds or removes an object and
  Shift+click selects a range.
- On the map, Ctrl/Shift+click toggles an object and Shift+drag draws a
  box that selects what lies wholly inside it (locked and hidden objects
  are left out).
- Ctrl+A selects everything that is not locked; Esc selects nothing.
- Clicking a wall or fence a second time selects every piece of the same
  type joined to it; another click goes back to that one piece.
- Dragging one selected object moves them all, together with the windows
  and doors on them, as one undo step. Arrow keys, R (turns the group
  about its middle), Ctrl+D, Delete, Lock and Hide all work on the whole
  selection.
- When all selected objects share a type, the property form edits them
  all; fields where they differ show "mixed".
- The agent's system prompt lists the selected objects.

The viewer outlines several objects with selectObj([ids]) and passes the
click event to onPick. A batch op now answers `ids`, one per operation,
so the copies from a group duplicate get selected.

Pond (Nature): natural, round or square, with a stone or grass edge,
fish, lily pads, spreading ripples and reed clumps. The fish come from a
new Swim primitive (script: s.swim). One matrix maps the object's frame
to the screen. Each fish turns round its ellipse with a CSS rotation,
so off-screen pausing and reduced motion apply as for the other
animations. The house demo gets a koi pond in the back garden.

Tests: ponds in every shape and rotation have the right number of fish,
no NaN and no depth-sort cycles, and stay inside their rectangle.
check_studio covers list and map multi-select, a group drag undone in
one step, joined-fence selection, a mixed-value form applied to all, box
select, delete and undo, Ctrl+A, Esc, and a new pond's fish.

crates/isokit-script/src/tests.rs

@@ -485,6 +485,63 @@ fn fences_join_like_walls_in_every_design() {
         .contains("iso-seam"));
 }
 
+#[test]
+fn ponds_have_fish_swimming_in_every_shape() {
+    let r = Runtime::new(&Bundle::default()).unwrap();
+    for (shape, edge, rot) in [
+        ("natural", "stone", 0.0),
+        ("round", "grass", 90.0),
+        ("square", "stone", 0.0),
+    ] {
+        let mut doc = Doc::default();
+        let mut o = obj(
+            "pond",
+            "pond",
+            3.0,
+            -2.0,
+            json!({"w": 9, "d": 5, "shape": shape, "edge": edge, "fish": 6, "lilies": 4}),
+        );
+        o.rot = rot;
+        doc.objects.push(o);
+        for view in 0..4u8 {
+            let b = r.build("site", view, &cfg(), &doc).unwrap();
+            assert!(
+                b.scene.warnings.is_empty(),
+                "{shape}: {:?}",
+                b.scene.warnings
+            );
+            let out = render(&b.scene, view, &RenderOpts::default());
+            assert_eq!(
+                out.html.matches("iso-a iso-swim").count(),
+                6,
+                "{shape}/{view}"
+            );
+            assert!(!out.html.contains("NaN"), "{shape}/{view}");
+            assert!(out.html.contains("iso-fish iso-koi") && out.html.contains("iso-lily"));
+            assert!(out.html.contains("iso-a iso-rip"));
+            assert_eq!(out.cycles, 0);
+        }
+        // the pond stays inside its 9 x 5 m (turned: 5 x 9 m) rectangle; the reeds stand on its edge
+        let bx = r.build("site", 0, &cfg(), &doc).unwrap().boxes["pond"];
+        let (hw, hd) = if rot == 0.0 { (4.5, 2.5) } else { (2.5, 4.5) };
+        assert!(
+            bx[0] >= 3.0 - hw - 1e-6
+                && bx[3] <= 3.0 + hw + 1e-6
+                && bx[1] >= -2.0 - hd - 1e-6
+                && bx[4] <= -2.0 + hd + 1e-6,
+            "{shape}: {bx:?}"
+        );
+    }
+    // no fish: no school
+    let mut doc = Doc::default();
+    doc.objects
+        .push(obj("p", "pond", 0.0, 0.0, json!({"fish": 0})));
+    let b = r.build("site", 0, &cfg(), &doc).unwrap();
+    assert!(!render(&b.scene, 0, &RenderOpts::default())
+        .html
+        .contains("iso-swim"));
+}
+
 #[test]
 fn site_walls_join_at_corners() {
     let r = Runtime::new(&Bundle::default()).unwrap();