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/shot/ShotDetailPanel.vue

@@ -301,6 +301,7 @@ interface Task extends TaskStatusInfo {
 interface Props {
   projectId: number
   shotId: number
+  initialShot?: Shot
 }
 
 interface Emits {
@@ -387,7 +388,7 @@ const loadShotDetails = async () => {
   try {
     isLoading.value = true
     error.value = null
-    shot.value = await shotService.getShot(props.shotId)
+    shot.value = props.initialShot ?? await shotService.getShot(props.shotId)
     loadTasks() // No longer async - uses embedded data
   } catch (err) {
     error.value = err instanceof Error ? err.message : 'Failed to load shot details'