feat: add dashboard, file preview metadata, and bandwidth statistics

Dashboard:
- Add DashboardDto, DashboardService with SQL-level aggregate queries
- Add GET /api/dashboard endpoint with real-time system status
- Add repository aggregate methods (CountByAvailability, SumDuration, etc.)
- Add DashboardView.vue as new landing page with KPI cards, storage status, recent sessions, top rooms
- Update router to make dashboard the new / route, add nav item in sidebar

File Preview:
- Add IVideoMetadataService + FfmpegVideoMetadataService for video metadata extraction
- Extend MediaBrowserItemDto with Metadata and ThumbnailUrl fields
- Add includeMetadata param to media browser API, add thumbnail endpoint
- Add SessionPlaylistDto and GET /api/record-sessions/{id}/playlist for continuous playback

Bandwidth Statistics:
- Add -progress pipe:1 to live recording ffmpeg args for bitrate output
- Parse total_size/bitrate/speed from ffmpeg progress lines during recording
- Write bandwidth samples as SystemLogEntry (Category=Bandwidth) every 30s
- Add BandwidthStatisticsService, BandwidthController with session timeline + daily summary
- Add bandwidth TypeScript types

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

src/LiveRecorder.Application/Services/BandwidthStatisticsService.cs

@@ -0,0 +1,135 @@
+using System.Text.Json;
+using LiveRecorder.Application.Abstractions.Persistence;
+using LiveRecorder.Application.Models.RecordTasks;
+using LiveRecorder.Domain.Enums;
+
+namespace LiveRecorder.Application.Services;
+
+public sealed class BandwidthStatisticsService
+{
+    private const string BandwidthCategory = "Bandwidth";
+    private const string SampleMessage = "bandwidth_sample";
+
+    private readonly ISystemLogRepository _systemLogRepository;
+
+    public BandwidthStatisticsService(ISystemLogRepository systemLogRepository)
+    {
+        _systemLogRepository = systemLogRepository;
+    }
+
+    public async Task<BandwidthTimelineDto?> GetSessionTimelineAsync(Guid recordSessionId, CancellationToken cancellationToken = default)
+    {
+        // Query all bandwidth sample log entries for this session
+        // Since there's no dedicated method, we use ListAsync with category filter
+        var allLogs = await _systemLogRepository.ListAllAsync(cancellationToken);
+        var bandwidthLogs = allLogs
+            .Where(item => item.Category == BandwidthCategory
+                           && item.Message == SampleMessage
+                           && item.RecordSessionId == recordSessionId)
+            .OrderBy(item => item.CreatedAt)
+            .ToList();
+
+        if (bandwidthLogs.Count == 0)
+        {
+            return null;
+        }
+
+        var points = new List<BandwidthPointDto>(bandwidthLogs.Count);
+        foreach (var entry in bandwidthLogs)
+        {
+            if (string.IsNullOrWhiteSpace(entry.Detail))
+            {
+                continue;
+            }
+
+            try
+            {
+                using var doc = JsonDocument.Parse(entry.Detail);
+                long bytesDownloaded = 0;
+                double? bitrateKbps = null;
+
+                if (doc.RootElement.TryGetProperty("bytesDownloaded", out var bd) && bd.TryGetInt64(out var bv))
+                    bytesDownloaded = bv;
+
+                if (doc.RootElement.TryGetProperty("bitrateKbps", out var br) && br.TryGetDouble(out var bkv))
+                    bitrateKbps = bkv;
+
+                points.Add(new BandwidthPointDto
+                {
+                    Timestamp = entry.CreatedAt,
+                    BytesDownloaded = bytesDownloaded,
+                    BitrateKbps = bitrateKbps
+                });
+            }
+            catch
+            {
+                // Skip malformed entries
+            }
+        }
+
+        return new BandwidthTimelineDto
+        {
+            RecordSessionId = recordSessionId,
+            Points = points
+        };
+    }
+
+    public async Task<BandwidthSummaryDto?> GetDailySummaryAsync(DateOnly date, int utcOffsetMinutes, CancellationToken cancellationToken = default)
+    {
+        var windowStartUtc = new DateTimeOffset(date.ToDateTime(TimeOnly.MinValue), TimeSpan.FromMinutes(utcOffsetMinutes));
+        var windowEndUtc = new DateTimeOffset(date.ToDateTime(TimeOnly.MaxValue), TimeSpan.FromMinutes(utcOffsetMinutes));
+
+        var allLogs = await _systemLogRepository.ListAllAsync(cancellationToken);
+        var bandwidthLogs = allLogs
+            .Where(item => item.Category == BandwidthCategory
+                           && item.Message == SampleMessage
+                           && item.CreatedAt >= windowStartUtc
+                           && item.CreatedAt <= windowEndUtc)
+            .OrderBy(item => item.CreatedAt)
+            .ToList();
+
+        if (bandwidthLogs.Count == 0)
+        {
+            return null;
+        }
+
+        var bitrates = new List<double>();
+        long maxBytes = 0;
+        long finalBytes = 0;
+
+        foreach (var entry in bandwidthLogs)
+        {
+            if (string.IsNullOrWhiteSpace(entry.Detail))
+                continue;
+
+            try
+            {
+                using var doc = JsonDocument.Parse(entry.Detail);
+                if (doc.RootElement.TryGetProperty("bytesDownloaded", out var bd) && bd.TryGetInt64(out var bv))
+                {
+                    if (bv > maxBytes) maxBytes = bv;
+                    finalBytes = bv;
+                }
+
+                if (doc.RootElement.TryGetProperty("bitrateKbps", out var br) && br.TryGetDouble(out var bkv))
+                {
+                    bitrates.Add(bkv);
+                }
+            }
+            catch
+            {
+                // Skip
+            }
+        }
+
+        var avgBitrate = bitrates.Count > 0 ? bitrates.Average() : 0;
+        var peakBitrate = bitrates.Count > 0 ? bitrates.Max() : 0;
+
+        return new BandwidthSummaryDto
+        {
+            TotalTrafficMB = finalBytes / (1024.0 * 1024.0),
+            AverageBitrateKbps = avgBitrate,
+            PeakBitrateKbps = peakBitrate
+        };
+    }
+}