[tintinhamans]

Moves logging to structured ILogger everywhere and adds OpenTelemetry logs, metrics and traces, exported over OTLP to a collector like Grafana Alloy. Sentry is optional and gets errors, plus logs and traces if enabled. Metrics only go over OTLP since Sentry 6.8 can't read .NET meters. Everything is off by default (OpenTelemetry:Enabled, Sentry:enabled), and docs/observability.md covers config, the metric list and an Alloy example.

Database, HTTP and runtime metrics come from the built-in MySqlConnector, ASP.NET Core, HttpClient and runtime meters. On top of that there are 14 genonline.* metrics worth alerting on: online players, active lobbies, auth attempts, WebSocket connections, failures and send queue depth, matchmaking queue, wait time and matches, background job failures and last success, external publication failures and backlog age, and security actions (rate limits, moderation, anti-cheat). Labels are small fixed sets, never player, lobby or match IDs.

Spans never carry SQL, connection strings or database users, and outbound HTTP spans only keep scheme, host and port since the TURN key is in the Cloudflare path. EF's command events are ignored in the context options, so SQL can't be logged whatever the logging config says. Slow commands (SlowDatabaseCommandMilliseconds, default 500) are logged with operation, duration and result only. Logs and traces do carry user, lobby and match IDs, so treat the collector and Sentry as holding player identifiers.

Builds on #80 (MySqlConnector advisory bump), so its commit stays in the diff until it lands. Lands before #77 and #71–#75, which build on it.

[Skyaero42]

This PR is doing a lot more than logging. Are you sure this PR is in line with the main branch?

[tintinhamans]

This PR is doing a lot more than logging. Are you sure this PR is in line with the main branch?

Was part of the stack before, made it based on main now.