feat: add tiered storage guard (Green/Yellow/Red) and dashboard queue monitor

Storage Tier System:
- Add StorageTier enum (Green >30% / Yellow 10-30% / Red <10%)
- Extend StorageGuardResult with Tier, CanStartNewRecording, ShouldPauseActive, UsagePercent
- Yellow tier: deny new recordings but allow existing to finish and upload
- Red tier: deny new recordings and pause active sessions
- Auto-recovery: when disk frees up, polling automatically resumes new recordings
- Update LiveRoomPollingBackgroundService to use tier-based checks
- Expose tier + usage percent in Recovery API

Dashboard Queue Monitor:
- Add pending transcode count, pending upload count, queued data volume to dashboard
- Add storage tier badge (Green/Yellow/Red) with usage percentage
- Add queue monitoring card to dashboard view

Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com

src/LiveRecorder.Infrastructure/Services/RecoveryService.cs

@@ -50,7 +50,9 @@ public sealed class RecoveryService
                 CheckedPath = storage.CheckedPath,
                 AvailableBytes = storage.AvailableBytes,
                 RequiredBytes = storage.RequiredBytes,
-                Message = storage.Message
+                Message = storage.Message,
+                Tier = storage.Tier.ToString(),
+                UsagePercent = storage.UsagePercent
             },
             LiveRooms = liveRooms,
             Finalizations = finalizations