Phase 1: standalone events, external_url on nodes

- Migration: node_id nullable on events and occurrences, add
  title/description/is_primary to events, external_url to nodes
- Existing events marked is_primary: true (were all 1:1 with nodes)
- Node: has_one :event -> has_many :events
- Event: belongs_to :node optional, validates title presence for
  standalone events, is_primary uniqueness scoped to node_id,
  display_title helper falling back through node title
- Occurrence: belongs_to :node optional, summary falls back to
  event.display_title
- nodes_helper: event_information uses events.first (interim; will
  be replaced in Phase 3 event UI)
- Tests: fix node.event -> node.events.first in event_test

1 files changed, 27 insertions, 0 deletions

diff --git a/db/migrate/20260627233640_upgrade_events_and_nodes_for_standalone_events.rb b/db/migrate/20260627233640_upgrade_events_and_nodes_for_standalone_events.rb
new file mode 100644
index 0000000..790a62b
--- /dev/null
+++ b/db/migrate/20260627233640_upgrade_events_and_nodes_for_standalone_events.rb
@@ -0,0 +1,27 @@
+class UpgradeEventsAndNodesForStandaloneEvents < ActiveRecord::Migration[8.1]
+  def up
+    # Events: make node optional, add missing fields
+    change_column_null :events, :node_id, true
+    add_column :events, :title,       :string
+    add_column :events, :description, :text
+    add_column :events, :is_primary,  :boolean, default: false, null: false
+
+    # Mark all existing events as primary (they were all 1:1 with nodes)
+    Event.where.not(node_id: nil).update_all(is_primary: true)
+
+    # Occurrences: make node optional
+    change_column_null :occurrences, :node_id, true
+
+    # Nodes: add external URL
+    add_column :nodes, :external_url, :string
+  end
+
+  def down
+    remove_column :nodes,       :external_url
+    change_column_null :occurrences, :node_id, false
+    remove_column :events, :is_primary
+    remove_column :events, :description
+    remove_column :events, :title
+    change_column_null :events, :node_id, false
+  end
+end