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/task.py

@@ -44,9 +44,9 @@ class Task(Base):
     id = Column(Integer, primary_key=True, index=True)
     project_id = Column(Integer, ForeignKey("projects.id"), nullable=False)
     episode_id = Column(Integer, ForeignKey("episodes.id"), nullable=True)
-    shot_id = Column(Integer, ForeignKey("shots.id"), nullable=True)
+    shot_id = Column(Integer, ForeignKey("shots.id"), nullable=True, index=True)
     asset_id = Column(Integer, ForeignKey("assets.id"), nullable=True)
-    assigned_user_id = Column(Integer, ForeignKey("users.id"), nullable=True)
+    assigned_user_id = Column(Integer, ForeignKey("users.id"), nullable=True, index=True)
     task_type = Column(String, nullable=False)  # Changed from Enum to String to support custom task types
     name = Column(String, nullable=False, index=True)
     description = Column(Text)
@@ -56,7 +56,7 @@ class Task(Base):
     updated_at = Column(DateTime(timezone=True), server_default=func.now(), onupdate=func.now())
     
     # Soft deletion columns
-    deleted_at = Column(DateTime(timezone=True), nullable=True)
+    deleted_at = Column(DateTime(timezone=True), nullable=True, index=True)
     deleted_by = Column(Integer, ForeignKey("users.id"), nullable=True)
 
     # Relationships