Optimize shot table loading performance

- Pass episode_id filter to backend API instead of client-side filtering,
  reducing payload size when an episode is selected
- Skip getShot refetch in ShotDetailPanel when initialShot prop is provided
- Fix redundant DB query in list_shots: read project.custom_task_statuses
  directly from the already-fetched project object
- Add missing indexes on Task.shot_id, Task.assigned_user_id,
  Task.deleted_at and Episode.project_id; add add_perf_indexes.py
  migration script to apply them to existing databases
- Center login page layout
- Update CLAUDE.md and AGENTS.md with correct venv path

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

frontend/src/components/layout/AppSidebar.vue

@@ -138,7 +138,7 @@ const isCollapsed = computed(() => state.value === 'collapsed')
 
 // Check if on shot page - show column switch only on shot pages
 const isOnShotPage = computed(() => {
-  return route.path.includes('/shots') || route.path.includes('/project/')
+  return route.path.endsWith('/shots') || route.path.includes('/project/')
 })
 
 const props = withDefaults(defineProps<SidebarProps>(), {