fix(maestro): swap focus rings for background tints on web

Focused sidebar rows and multiview panes drew a green border/ring.
Swap to a background tint on the row and the pane titlebar instead,
so focus stays borderless.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/styles.css

@@ -761,7 +761,7 @@ textarea {
 
 .tree-leaf:focus-visible {
   outline: none;
-  box-shadow: inset 0 0 0 1px var(--accent-ring);
+  background: color-mix(in oklab, var(--accent) 16%, var(--surface-2));
 }
 
 /* Where the keyboard walk (j/k) is standing. Distinct from `.is-active`: this
@@ -2353,10 +2353,9 @@ input.leaf-rename:focus {
   min-width: 0;
   min-height: 0;
 }
-/* focused pane: accent ring, full strength */
-.mv-pane.is-focused {
-  border-color: var(--accent);
-  box-shadow: inset 0 0 0 1px var(--accent);
+/* focused pane: titlebar tints instead of a ring, full strength */
+.mv-pane.is-focused .attach-header {
+  background: color-mix(in oklab, var(--accent) 14%, var(--surface));
 }
 /* unfocused panes recede so the eye finds the live one */
 .mv-pane:not(.is-focused) {