test: avoid disk-bound history limit fixtures

Use real in-memory SQLite for the remote-message ordering and active-task
retention query tests. Both exceeded the CI five-second limit while seeding
502 independently committed records on disk.

Keep the record counts, public database calls, and assertions unchanged.
Disk persistence, transactional migration, and reopen tests remain disk-backed.
Production database behavior is unchanged.

src/main/assistant/assistant-database.test.ts

@@ -1965,8 +1965,10 @@ describe('AssistantDatabase', () => {
     database.close()
   })
 
-  it('returns the latest 500 remote messages in chronological order', async () => {
-    const database = await createDatabase()
+  it('returns the latest 500 remote messages in chronological order', () => {
+    // Exercise the query boundary without 502 disk-synchronized fixture writes.
+    const database = new AssistantDatabase(':memory:')
+    database.initialize('C:\\Workspace')
     const project = database.ensureChannelProjects(
       'C:\\Users\\test',
       channelDefaultProfileId

src/main/knowledge/knowledge-database.test.ts

@@ -621,8 +621,11 @@ describe('KnowledgeDatabase', () => {
     })
   })
 
-  it('lists every active task in addition to the terminal history limit', async () => {
-    const { database } = await createDatabase()
+  it('lists every active task in addition to the terminal history limit', () => {
+    // This checks retention, not the disk latency of 502 independent writes.
+    const database = new KnowledgeDatabase(':memory:')
+    database.initialize()
+    openDatabases.push(database)
     const library = database.createKnowledgeBase({
       name: 'Task listing',
       storageMode: 'reference'