fix: replace InfoTooltip v-tooltip with v-menu popover card

v-tooltip renders a forced-dark background unsuitable for multi-line
help content. Switch to v-menu + v-card which follows the app theme.
Use surface-variant background for the "Tip:" block.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/app/src/components/sections/CreateShiftDialog.vue

@@ -250,7 +250,10 @@ function onSubmit() {
                 >
                   <InfoTooltip>
                     <p>{{ tooltipText?.main }}</p>
-                    <div class="mt-2 pa-2 bg-surface rounded text-caption">
+                    <div
+                      class="mt-2 pa-2 rounded text-caption"
+                      style="background: rgb(var(--v-theme-surface-variant)); line-height: 1.5;"
+                    >
                       <strong>Tip:</strong> {{ tooltipText?.tip }}
                     </div>
                   </InfoTooltip>