Let a blank tree label take the click as well as draw the caret

The class fix rendered the `+` but the node still would not open, and the
caret did not light on hover. `tbody th:empty { pointer-events: none }`
makes the padding cells left of a tree label inert, and a label cell whose
group key is null or "" is `:empty` too — its caret is a `::before`, which
does not count as content — so the cell received no pointer events at all.

Exclude the tree classes from that rule. `row-hover.css` reads `:empty` the
same way in six border selectors; those are a hover tint, left alone.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/package-lock.json

@@ -578,7 +578,7 @@
     "node_modules/@perspective-dev/client": {
       "version": "5.4.0",
       "resolved": "file:vendor/perspective-dev-client-5.4.0.tgz",
-      "integrity": "sha512-e1rkiCyIlEwSFcEmw/KuNOnrX0k6UiMfnvQB8nwQfkKtoW5d1hkveQ8lAGsj8UZskJuuHrxpWpnKnFm2bwBV7A==",
+      "integrity": "sha512-d6TKVh6DFKuGpiLYN2PmA8U9GbkMtgiCy9iUrLx7STMABT2kYwUE4tVQLqm/sRlwcRiVJ4+K2d1l6J8cgX+6Aw==",
       "license": "Apache-2.0",
       "dependencies": {
         "@perspective-dev/server": "^5.4.0",
@@ -596,7 +596,7 @@
     "node_modules/@perspective-dev/viewer": {
       "version": "5.4.0",
       "resolved": "file:vendor/perspective-dev-viewer-5.4.0.tgz",
-      "integrity": "sha512-dioznGFDoR2fx+0JBdg4SP/WWUxcCeZ9XrKuUiYOgJaXYadegESS0yr1rhMbMNJlG9IQzBCi/WFOvKKzcxkJJA==",
+      "integrity": "sha512-AkQwfacQFSJ0fZ7Ja142pa0HGLssxFK9/FM4jhrMvrXp31Rp74qRNIyueG8wiqGTPXmORaRDA+ePtW+Wfg5UpA==",
       "license": "Apache-2.0",
       "dependencies": {
         "@perspective-dev/client": "^5.4.0",
@@ -607,7 +607,7 @@
     "node_modules/@perspective-dev/viewer-datagrid": {
       "version": "5.4.0",
       "resolved": "file:vendor/perspective-dev-viewer-datagrid-5.4.0.tgz",
-      "integrity": "sha512-J5UL8GNqi5rrmeiOpyGanosSTxRi2bwHNxEHode/DMRP55FEMt+gMVqkC/LfuINi1b0TKVtJQCP+UN8MlnGgpw==",
+      "integrity": "sha512-7wqr7T8cp6SI1ZZy69qy0Y6sZ5UJCpQjHPnDL6Fjs3ATJtmhmVEz/dpcMcjCgqwGrs5Sqd7xyKNQ+RuwcBsMEQ==",
       "license": "Apache-2.0",
       "dependencies": {
         "@perspective-dev/client": "^5.4.0",

ui/vendor/PROVENANCE.txt

@@ -1,8 +1,8 @@
 Built from https://github.com/fleetside72/perspective
   branch  expand-blank-tree-nodes
-  commit  40266dc6ec4d83895483124386f0c79938d639ca
+  commit  751dcfe136c6455e3cd02a7b75a6df79cbe8e064
   based on unknown
-  built   2026-09-22T04:06:28Z on usmidsap02
+  built   2026-09-22T04:18:51Z on usmidsap02
   dirty   0 uncommitted file(s) in the source tree at build time
 
 Regenerate with ui/vendor/rebuild-perspective.sh

ui/vendor/README.md

@@ -102,6 +102,17 @@ following row. Flat rollup (`group_rollup_mode: 'flat'`) writes each level into
 its own cell with no padding, so there is nothing structural to test there and
 it keeps the text test.
 
+The class was only half of it. `tbody th:empty { pointer-events: none }` in
+`regular_table.css` makes the padding cells inert, and a blank label cell is
+`:empty` as well — a `::before` caret is not content — so the fixed node drew
+its `+`, then ignored the click and would not even take the hover. The rule now
+excludes the tree classes, which is the distinction it was reaching for: a
+padding cell never carries one.
+
+`row-hover.css` uses `:empty` the same way in six border selectors. Those are a
+hover tint and are left alone; a row whose first level is blank loses a border
+highlight, and nothing else.
+
 Separate from the data question: null and `''` group as two distinct rows that
 look identical, so a `COALESCE(NULLIF(col,''), '(none)')` at load time is still
 worth doing on its own merits.