Sticky table headers, layout parity, and reuse My Tasks on the shared table/toolbar

Shot/Asset/Task data tables now keep their header row pinned while scrolling
(both the locked two-pane and single-table modes), matching a common data-
table expectation that was missing everywhere.

Brings Asset and Task browsers to full structural parity with Shot's bounded-
height layout (fixed toolbar, internally-scrolling table) instead of their
previous page-scroll model with a sticky-positioned toolbar. AssetsDataTable
gained the synced frozen/movable-pane scrolling it was missing entirely;
TasksDataTable and both browsers/parent views got the same container model.

The global My Tasks page (/tasks) now reuses TaskTableToolbar and
TasksDataTable instead of its own ad hoc filter selects and TaskList,
including the detail panel, bulk status/assignment context menu, and sticky
header for free. Since it spans multiple projects, TaskTableToolbar gained
an optional Project filter (only rendered when a project list is passed in,
so the project-scoped Tasks page is unaffected); episode/assignee filters
populate once a specific project is chosen.

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

frontend/src/components/shot/ShotsDataTable.vue

@@ -7,7 +7,7 @@
           <!-- Left pane: frozen columns (no horizontal scroll, vertical scroll hidden + synced) -->
           <div ref="leftPane" class="flex-shrink-0 h-full overflow-y-auto scrollbar-hide border-r" @scroll="onLeftScroll">
             <table class="caption-bottom text-sm">
-              <TableHeader>
+              <TableHeader class="sticky top-0 z-10 bg-background">
                 <TableRow v-for="headerGroup in table.getHeaderGroups()" :key="headerGroup.id">
                   <TableHead
                     v-for="header in frozenHeaders(headerGroup)"
@@ -51,7 +51,7 @@
           <!-- Right pane: movable columns (own horizontal scrollbar, only shown when needed) -->
           <div ref="rightPane" class="flex-1 min-w-0 h-full overflow-auto" @scroll="onRightScroll">
             <table class="min-w-full caption-bottom text-sm">
-              <TableHeader>
+              <TableHeader class="sticky top-0 z-10 bg-background">
                 <TableRow v-for="headerGroup in table.getHeaderGroups()" :key="headerGroup.id">
                   <TableHead
                     v-for="header in movableHeaders(headerGroup)"
@@ -102,7 +102,7 @@
 
       <!-- Unlocked: standard single table -->
       <Table v-else>
-        <TableHeader>
+        <TableHeader class="sticky top-0 z-10 bg-background">
           <TableRow v-for="headerGroup in table.getHeaderGroups()" :key="headerGroup.id">
             <TableHead
               v-for="header in headerGroup.headers"