test: add frontend composable tests — useNostr (9), useFightCache (5), useOnlineStatus (4)

Tests cover login state, logout, signer detection, key persistence, IndexedDB
caching/eviction, online/offline detection, and singleton pattern.

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

pnpm-lock.yaml

@@ -61,6 +61,9 @@ importers:
       '@vue/test-utils':
         specifier: ^2.4.6
         version: 2.4.6
+      fake-indexeddb:
+        specifier: ^6.2.5
+        version: 6.2.5
       jsdom:
         specifier: ^28.1.0
         version: 28.1.0(@noble/hashes@2.0.1)
@@ -2210,6 +2213,10 @@ packages:
     resolution: {integrity: sha512-knvyeauYhqjOYvQ66MznSMs83wmHrCycNEN6Ao+2AeYEfxUIkuiVxdEa1qlGEPK+We3n0THiDciYSsCcgW/DoA==}
     engines: {node: '>=12.0.0'}
 
+  fake-indexeddb@6.2.5:
+    resolution: {integrity: sha512-CGnyrvbhPlWYMngksqrSSUT1BAVP49dZocrHuK0SvtR0D5TMs5wP0o3j7jexDJW01KSadjBp1M/71o/KR3nD1w==}
+    engines: {node: '>=18'}
+
   fast-deep-equal@3.1.3:
     resolution: {integrity: sha512-f3qQ9oQy9j2AhBe/H9VC91wLmKBCCU/gDOnKNAYG5hswO7BLKj09Hc5HYNz9cGI++xlpDCIgDaitVs03ATR84Q==}
 
@@ -5835,6 +5842,8 @@ snapshots:
 
   expect-type@1.3.0: {}
 
+  fake-indexeddb@6.2.5: {}
+
   fast-deep-equal@3.1.3: {}
 
   fast-json-stable-stringify@2.1.0: {}