feat(sidechat): tool-kind leading icons on tool rows

The main conversation's tool row head is a 16px leading slot with the
tool-kind glyph at 14 (GenericToolCard's variant table), swapped for an
error StateDot on failed rows. Mirror it: bash/pwsh -> IconApiOutline14,
read/web_fetch -> IconBrowseOutline16, edit/write -> IconEditOutline16,
grep/glob/web_search -> IconSearchOutline16, anything else ->
IconSparkle16, all from the ui-primitives module seed; CollapsibleRow
gains the matching icon slot. Thinking/injection rows keep their bare
chrome (the host's equivalents are a different row family).

src/client/SideChatView.module.css

@@ -221,6 +221,18 @@
   transform: rotate(90deg);
 }
 
+/* Tool-kind leading glyph (the main conversation's 16px slot; the icon
+ * itself renders at 14). Failed rows pass a StateDot instead. */
+.sidechatRowIcon {
+  flex: none;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: 16px;
+  height: 16px;
+  color: var(--dsw-alias-label-tertiary);
+}
+
 .sidechatRowLabel {
   flex: none;
   max-width: 60%;