feat: Event archive management — Event model, migration, API, frontend page (Phase 8)

- Event ORM model with status/level enums, domain categories, review tracking
- Alembic migration e7f3a9b1c5d0 for events table
- Event crawler service with placeholder data (12 sample events)
- GET /api/v1/events with status/domain/search filtering and overdue_days
- EventArchivePage with filter toolbar (status, domain, search) and adaptive card grid
- Status badges, level badges, domain tags, overdue markers on event cards
- Loading/error/empty states, hover-to-honey card interaction

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

backend/alembic/versions/e7f3a9b1c5d0_create_events_table.py

@@ -0,0 +1,46 @@
+"""create events table
+
+Revision ID: e7f3a9b1c5d0
+Revises: ab0c56ae4242
+Create Date: 2026-07-22 17:30:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'e7f3a9b1c5d0'
+down_revision: Union[str, Sequence[str], None] = 'ab0c56ae4242'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        'events',
+        sa.Column('id', sa.String(36), primary_key=True),
+        sa.Column('title', sa.String(255), nullable=False),
+        sa.Column('level', sa.Enum('A', 'B', 'C', name='eventlevel'), nullable=False),
+        sa.Column('domain', sa.String(50), nullable=False, index=True),
+        sa.Column(
+            'status',
+            sa.Enum('active', 'fading', 'dissipating', 'closed', name='eventstatus'),
+            nullable=False,
+            server_default='active',
+        ),
+        sa.Column('occurred_date', sa.Date, nullable=False),
+        sa.Column('last_reviewed', sa.DateTime, nullable=True),
+        sa.Column('no_new_info_count', sa.Integer, nullable=False, server_default='0'),
+        sa.Column('next_review', sa.DateTime, nullable=True),
+        sa.Column('created_at', sa.DateTime, nullable=False, server_default=sa.func.now()),
+        sa.Column('updated_at', sa.DateTime, nullable=False, server_default=sa.func.now()),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table('events')
+    op.execute('DROP TYPE IF EXISTS eventlevel')
+    op.execute('DROP TYPE IF EXISTS eventstatus')