fix: replace silent error swallowing with console.warn and user-facing error messages

All empty catch blocks across 8 Vue pages now log warnings. User-initiated
actions (fight, matchmake) also surface errors in the UI via fightError/loadError refs.

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

frontend/src/pages/HomePage.vue

@@ -304,7 +304,9 @@ onMounted(async () => {
       const data = await res.json()
       recentFights.value = data.slice(0, 4)
     }
-  } catch { /* server not running */ }
+  } catch (err) {
+    console.warn('[Home] load fights failed:', err)
+  }
 })
 
 onUnmounted(() => {