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>

backend/models/episode.py

@@ -17,7 +17,7 @@ class Episode(Base):
     __tablename__ = "episodes"
 
     id = Column(Integer, primary_key=True, index=True)
-    project_id = Column(Integer, ForeignKey("projects.id"), nullable=False)
+    project_id = Column(Integer, ForeignKey("projects.id"), nullable=False, index=True)
     name = Column(String, nullable=False, index=True)
     description = Column(String)
     episode_number = Column(Integer, nullable=False)