Add conditional boss battle teams (variant teams by condition)

Wire up the existing condition_label column on boss_pokemon to support
variant teams throughout the UI. Boss battles can now have multiple team
configurations based on conditions (e.g., starter choice in Gen 1).

- Add condition_label to BossPokemonInput schema (frontend + backend bulk import)
- Rewrite BossTeamEditor with variant tabs (Default + named conditions)
- Add variant pill selector to BossDefeatModal team preview
- Add BossTeamPreview component to RunEncounters boss cards
- Fix MissingGreenlet error in set_boss_team via session.expunge_all()
- Fix PokemonSelector state bleed between tabs via composite React key
- Add Alembic migration for condition_label column

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

.beans/nuzlocke-tracker-x8ol--starter-dependent-boss-battle-teams.md

@@ -1,11 +1,11 @@
 ---
 # nuzlocke-tracker-x8ol
 title: Conditional boss battle teams
-status: draft
+status: in-progress
 type: feature
 priority: normal
 created_at: 2026-02-08T13:23:00Z
-updated_at: 2026-02-08T13:29:26Z
+updated_at: 2026-02-08T19:34:27Z
 ---
 
 Some boss battles have teams that vary based on conditions in the player's run. The most common case is starter choice (e.g., Blue's team in Gen 1 depends on whether you picked Bulbasaur, Charmander, or Squirtle), but other conditions exist too — in Pokemon Yellow, the rival's team changes based on the outcomes of two early-game fights, not the starter. This feature adds support for defining multiple team variants per boss battle, each associated with a named condition.