Add pokemon status management with death tracking

Implement status change workflow (alive → dead) with confirmation modal,
death cause recording, and visual status indicators on pokemon cards.
Includes backend migration for death_cause field and graveyard view
on the run dashboard.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/app/alembic/versions/a1b2c3d4e5f6_add_death_cause_to_encounters.py

@@ -0,0 +1,26 @@
+"""add death_cause to encounters
+
+Revision ID: a1b2c3d4e5f6
+Revises: 9afcbafe9888
+Create Date: 2026-02-05 17:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'a1b2c3d4e5f6'
+down_revision: Union[str, Sequence[str], None] = '9afcbafe9888'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column('encounters', sa.Column('death_cause', sa.String(100), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column('encounters', 'death_cause')