feat: make level field optional in boss defeat modal

Remove the level input from the boss defeat modal since the app doesn't
track levels elsewhere. Team selection is now just checkboxes without
requiring level entry.

- Remove level input UI from BossDefeatModal.tsx
- Add alembic migration to make boss_result_team.level nullable
- Update model and schemas to make level optional (defaults to null)
- Conditionally render level in boss result display

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

.beans/nuzlocke-tracker-532i--ux-remove-level-field-from-boss-defeat-modal.md

@@ -1,11 +1,11 @@
 ---
 # nuzlocke-tracker-532i
 title: 'UX: Make level field optional in boss defeat modal'
-status: todo
+status: completed
 type: feature
 priority: normal
 created_at: 2026-03-21T21:50:48Z
-updated_at: 2026-03-21T22:04:08Z
+updated_at: 2026-03-22T09:16:12Z
 ---
 
 ## Problem
@@ -22,8 +22,17 @@ When recording which team members beat a boss, users must manually enter a level
 
 Remove the level field entirely from the UI and make it optional in the backend:
 
-- [ ] Remove level input from `BossDefeatModal.tsx`
-- [ ] Make `level` column nullable in the database (alembic migration)
-- [ ] Update the API schema to make level optional (default to null)
-- [ ] Update any backend validation that requires level
-- [ ] Verify boss result display still works without level data
+- [x] Remove level input from `BossDefeatModal.tsx`
+- [x] Make `level` column nullable in the database (alembic migration)
+- [x] Update the API schema to make level optional (default to null)
+- [x] Update any backend validation that requires level
+- [x] Verify boss result display still works without level data
+
+
+## Summary of Changes
+
+- Removed level input field from BossDefeatModal.tsx, simplifying team selection to just checkboxes
+- Created alembic migration to make boss_result_team.level column nullable
+- Updated SQLAlchemy model and Pydantic schemas to make level optional (defaults to null)
+- Updated RunEncounters.tsx to conditionally render level only when present
+- Updated frontend TypeScript types for BossResultTeamMember and BossResultTeamMemberInput