Add structured logging to silently swallowed catch blocks

[devin-ai-integration]

Summary

Several best-effort catch blocks swallowed exceptions with no logging at all — a Redis hiccup, a failed audit write, or a quota-release error would vanish silently, making production diagnosis impossible. This PR injects ILogger<T> into those services and adds structured log calls so every swallowed failure leaves a trace.

What changed (all catches remain non-fatal — only visibility is added):

# RedisCachePurge — cache purge failures were invisible
- catch (Exception) when (!ct.IsCancellationRequested) { }
+ catch (Exception ex) when (!ct.IsCancellationRequested)
+   logger.LogWarning(ex, "Cache purge failed for prefix '{Prefix}'", prefix);

# JobService.TransitionAsync — audit-write failures were invisible
- catch (Exception ex) when (ex is not OperationCanceledException) { }
+ catch (...) { logger.LogWarning(ex, "Audit write failed for upload.{State} on job {JobId}", to, job.Id); }

# QuotaService.ChargeUnitsAsync — Redis metering failures were invisible
- catch { /* best-effort meter */ }
+ catch (Exception ex) { logger.LogWarning(ex, "Quota unit charge failed for project {ProjectId}", projectId); }

# GoogleAccountsService.ExchangeAndStoreAsync — channel lookup failures were invisible
- catch { /* channel lookup is best-effort */ }
+ catch (Exception ex) { logger.LogWarning(ex, "Channel lookup failed during OAuth exchange for project {ProjectId}", projectId); }

# UploadJobHandler — three bare catch blocks for quota release / MarkAccountError
- catch { /* best effort */ }
+ catch (Exception qex) { logger.LogDebug(qex, "Best-effort quota release failed ..."); }
+ catch (Exception aex) { logger.LogWarning(aex, "Best-effort MarkAccountError failed ..."); }

# YouTubeUploadsProviderEndpoints OAuth start — BuildConsentUrlAsync failure was unlogged
+ loggerFactory.CreateLogger("YouTubeUploads.Google.OAuth").LogError(ex, "Google OAuth start failed for project {ProjectId}", projectId.Value);

Test constructors updated to pass NullLogger<T>.Instance for the new parameters. All 234 tests pass.

Link to Devin session: https://app.devin.ai/sessions/0b54f37fe20049d0a218def75b07b0c0
Requested by: @skyp1nus

[devin-ai-integration]

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