feat: add topic hierarchy APIs

tests/migrations.test.ts

@@ -16,7 +16,7 @@ afterEach(async () => {
 });
 
 describe('initializeSchema', () => {
-  it('creates the topics, facts, and fact_topics tables', async () => {
+  it('creates the topics, facts, fact_topics, and topic_relations tables', async () => {
     const connection = await createDatabase({ client: 'sqlite', filename: ':memory:' });
     openConnections.push(connection.destroy);
 
@@ -34,6 +34,7 @@ describe('initializeSchema', () => {
     expect(tableNames).toContain('topics');
     expect(tableNames).toContain('facts');
     expect(tableNames).toContain('fact_topics');
+    expect(tableNames).toContain('topic_relations');
   });
 
   it('creates the expected columns for each table', async () => {
@@ -45,6 +46,7 @@ describe('initializeSchema', () => {
     const topicsColumns = await sql<{ name: string }>`PRAGMA table_info(topics)`.execute(connection.db);
     const factsColumns = await sql<{ name: string }>`PRAGMA table_info(facts)`.execute(connection.db);
     const factTopicsColumns = await sql<{ name: string }>`PRAGMA table_info(fact_topics)`.execute(connection.db);
+    const topicRelationsColumns = await sql<{ name: string }>`PRAGMA table_info(topic_relations)`.execute(connection.db);
 
     expect(topicsColumns.rows.map((row) => row.name)).toEqual([
       'id',
@@ -76,6 +78,13 @@ describe('initializeSchema', () => {
       'position',
       'created_at',
     ]);
+
+    expect(topicRelationsColumns.rows.map((row) => row.name)).toEqual([
+      'parent_topic_id',
+      'child_topic_id',
+      'relation',
+      'created_at',
+    ]);
   });
 
   it('is idempotent when called more than once', async () => {