fix: Add missing updated_at column to epics table

epic_close was failing with "column updated_at does not exist".
Migration adds the column with default NOW() and backfills
existing rows from created_at.

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

migrations/005_epics_updated_at.sql

@@ -0,0 +1,7 @@
+-- Migration 005: Add updated_at column to epics table
+-- Fixes: epic_close error "column updated_at does not exist"
+
+ALTER TABLE epics ADD COLUMN IF NOT EXISTS updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW();
+
+-- Set existing rows to created_at value
+UPDATE epics SET updated_at = created_at WHERE updated_at IS NULL;