Select a range of rows with shift-click in the hierarchy (#241)

Ctrl- and shift-click only added single rows to the selection. With
many objects spread over the hierarchy, picking a run of them meant
clicking each one. Shift-click now selects everything between the
anchor and the clicked row, as in a file explorer.

- The anchor is the row last clicked without shift, plain or with
  ctrl. A second shift-click redraws the range from the same anchor.
- Ctrl+shift-click adds the range to the current selection instead
  of replacing it.
- A collapsed group inside the range brings all its members. Children
  hidden under a collapsed parent stay out, since they are not shown.
- Without an anchor from the hierarchy, the primary object picked in
  the scene view serves as anchor. With no selection at all,
  shift-click adds the single row as before.
- The range rule is a pure function in hierarchyRange.ts, so it is
  tested without a browser. HierarchyPanel keeps the anchor.

Not checked in the browser: ctrl+shift-click and the anchor taken from
the scene view. Only the code path covers them.

Tests:
- ./check.sh: 178 files, 2557 tests, CHECK EXIT 0
- e2e 1 + 52: ALL PASSED, 23 checks
- 5 new unit tests in tests/editor/hierarchy-range.test.ts
- New e2e check 52h with real clicks
- Counter-check: without the range, 52h fails with ["o2","o5"]

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -43,7 +43,7 @@ npm run build        # writes dist/ and regenerates index.html; the folder is wh
 The browser suite and the three example games need a machine with a GPU:
 
 ```bash
-node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1442 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1443 checks (GM_STEPS=20 for one step)
                                                    #   every tool signs in first – see the Accounts page
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs