test: add frontend composable tests and remaining test files

useNostr (9), useFightCache (5), useOnlineStatus (4) composable tests.
Added fake-indexeddb dev dependency for IDB tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/engine/events.test.ts

@@ -0,0 +1,58 @@
+import { describe, it, expect } from 'vitest'
+import { fightEvents, type FightEvent } from './events.js'
+
+describe('fightEvents', () => {
+  it('emits events to fight-specific listeners', () => {
+    const events: FightEvent[] = []
+    const unsub = fightEvents.on('fight-1', (e) => events.push(e))
+
+    fightEvents.emit({
+      fightId: 'fight-1',
+      type: 'test',
+      data: { msg: 'hello' },
+      timestamp: new Date().toISOString(),
+    })
+
+    expect(events).toHaveLength(1)
+    expect(events[0].data.msg).toBe('hello')
+    unsub()
+  })
+
+  it('cleanup removes all listeners for a fight', () => {
+    const events: FightEvent[] = []
+    fightEvents.on('fight-cleanup', (e) => events.push(e))
+    fightEvents.on('fight-cleanup', (e) => events.push(e))
+
+    fightEvents.cleanup('fight-cleanup')
+
+    fightEvents.emit({
+      fightId: 'fight-cleanup',
+      type: 'test',
+      data: {},
+      timestamp: new Date().toISOString(),
+    })
+
+    expect(events).toHaveLength(0)
+  })
+
+  it('global listeners receive all events', () => {
+    const events: FightEvent[] = []
+    const unsub = fightEvents.onAll((e) => events.push(e))
+
+    fightEvents.emit({
+      fightId: 'fight-global-1',
+      type: 'test',
+      data: {},
+      timestamp: new Date().toISOString(),
+    })
+    fightEvents.emit({
+      fightId: 'fight-global-2',
+      type: 'test',
+      data: {},
+      timestamp: new Date().toISOString(),
+    })
+
+    expect(events).toHaveLength(2)
+    unsub()
+  })
+})