fix(frontend) : fix time-tracking page scroll with fixed header and filters

Restructure time-tracking page layout so the page title and filters
stay fixed while only the calendar grid body scrolls internally.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/components/time-tracking/TimeTrackingCalendar.vue

@@ -1,9 +1,8 @@
 <template>
-    <div ref="calendarEl" class="relative rounded-lg border border-neutral-200 bg-white">
+    <div ref="calendarEl" class="relative flex h-full flex-col rounded-lg border border-neutral-200 bg-white">
         <!-- Day headers -->
         <div
-            class="sticky z-20 flex border-b border-neutral-200 bg-white"
-            :style="{ top: `${stickyOffset}px` }"
+            class="z-20 flex flex-shrink-0 border-b border-neutral-200 bg-white rounded-t-lg"
         >
             <div class="w-16 shrink-0 border-r border-neutral-200" />
             <div
@@ -22,7 +21,7 @@
         </div>
 
         <!-- Grid body -->
-        <div ref="gridBodyEl" class="relative flex">
+        <div ref="gridBodyEl" class="relative flex min-h-0 flex-1 overflow-y-auto">
             <!-- Hour labels -->
             <div class="w-16 shrink-0">
                 <div