fix(tooltip): pull the caret base into the panel to hide the border seam

A perceptible line showed across the caret base on every side but bottom: the
panel's border draws across the caret's base edge, "cutting" it off from the panel.
Add the popover's per-side fix — pull the caret base into the panel by the border
width (margin toward the panel, keyed on data-side) so the fill covers that border
and the caret's side strokes continue the panel outline seamlessly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/uix/eidos/components/tooltip/tooltip.css

@@ -103,6 +103,23 @@
 	vector-effect: non-scaling-stroke;
 }
 
+/* Pull the caret base into the panel by the border width (per side) so the fill
+ * covers the panel's border there and the side strokes continue the outline —
+ * otherwise the panel border draws a line across the caret base. Mirrors the
+ * popover recipe. */
+[data-tooltip-arrow][data-side='bottom'] {
+	margin-block-start: var(--tooltip-border-width);
+}
+[data-tooltip-arrow][data-side='top'] {
+	margin-block-end: var(--tooltip-border-width);
+}
+[data-tooltip-arrow][data-side='left'] {
+	margin-inline-end: var(--tooltip-border-width);
+}
+[data-tooltip-arrow][data-side='right'] {
+	margin-inline-start: var(--tooltip-border-width);
+}
+
 /* Outline variant: transparent bg → fill with the surface, stroke the edges. */
 [data-tooltip-content][data-variant='outline'] ~ [data-tooltip-arrow] polygon,
 [data-tooltip-content][data-variant='outline'] [data-tooltip-arrow] polygon {