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/HumanFightPage.vue

@@ -171,7 +171,9 @@ async function loadFight() {
         enemyHp.value = amSideA.value ? data.botBHp : data.botAHp
       }
     }
-  } catch { /* */ }
+  } catch (err) {
+    console.warn('[HumanFight] poll failed:', err)
+  }
 }
 
 function watchReplay() {