Enhance logging in FdsSqlOptions and related classes

- Updated FdsSqlOptions to accept an optional ILogger parameter for improved error logging.
- Modified FdsMfr and FdsMfrClient classes to pass the logger instance to FdsSqlOptions.
- Added detailed error logging in various methods to capture SQL execution issues and file handling errors.
- Improved documentation for FdsSqlOptions to clarify logging behavior.
- Updated Archive class to log compression errors, enhancing traceability of failures.
- Adjusted project configuration to suppress specific warnings related to transitive dependencies.
- Added NuGet.config to define package sources for dependency management.
- Updated submodule references for OCORE and related projects.

Fuchs/Docs/Decisions/0004-opentelemetry-observability.md

@@ -0,0 +1,65 @@
+---
+status: Accepted
+date: 2026-07-03
+applyTo:
+  - "Fuchs/Observability/**"
+  - "Fuchs/Program.cs"
+  - "Fuchs/Services/**"
+supersededBy: ""
+---
+
+# 0004 — OpenTelemetry is wired in extensively, without compromising performance
+
+## Context
+Beyond text logs (see [0003](0003-structured-diagnostic-logging.md)), the
+solution needs distributed tracing and metrics to understand performance and
+behavior in production (PDF render durations, email send outcomes, MFR call
+volume, banking import throughput) without depending on a debugger or manual
+log-grepping — while never letting the absence of a collector break or slow
+down the app.
+
+## Decision
+- All instrumentation is centralized in `Fuchs/Observability/FuchsTelemetry.cs`:
+  one `ActivitySource` (`Fuchs.Intranet`) for tracing and one `Meter` for
+  metrics, exposing named `Counter<long>`/`Histogram<double>` instruments
+  (invoices/reminders/reports rendered, emails/SMS sent/failed, MT940 rows
+  parsed, banking entries skipped/truncated, MFR calls, blob upload
+  success/failure, PDF/report/email durations) plus a `StartActivity` helper.
+- Wired in `Program.cs` behind `Fuchs:Telemetry:Enabled` (default `true`):
+  `AddOpenTelemetry()` with `AddAspNetCoreInstrumentation`,
+  `AddHttpClientInstrumentation`, `AddSqlClientInstrumentation` for tracing,
+  and `AddAspNetCoreInstrumentation`, `AddHttpClientInstrumentation`,
+  `AddRuntimeInstrumentation` for metrics.
+- **Collection is always on; export is opt-in.** The OTLP exporter is only
+  added when `Fuchs:Telemetry:OtlpEndpoint` is configured — with no
+  collector present, spans/metrics are simply collected in-process and
+  discarded, so a missing collector can never cause startup failures,
+  exceptions, or blocking calls. Setting `Fuchs:Telemetry:Enabled=false`
+  disables instrumentation entirely.
+- Per the project-wide Observability standard: every meaningful operation
+  starts an activity via `FuchsTelemetry.StartActivity(...)`, records the
+  matching counter/histogram, and logs entry/result/timing/errors via
+  injected `ILogger<T>` with structured placeholders — this is enforced for
+  new service/handler code, not just the initial wiring.
+
+## Consequences
+- New business operations worth observing must add a named instrument to
+  `FuchsTelemetry.cs` rather than creating ad-hoc `ActivitySource`/`Meter`
+  instances elsewhere — one source, one meter, keeps exporters and
+  dashboards simple.
+- Because export is opt-in, local/dev environments get full in-process
+  instrumentation with zero setup; wiring an OTLP collector is purely an
+  ops-side configuration change (`Fuchs:Telemetry:OtlpEndpoint`), not a
+  code change.
+- Instrumentation must stay cheap on the hot path — use the existing
+  counters/histograms rather than allocating new tags/dictionaries per call
+  where avoidable, and never make a business operation depend on the
+  exporter succeeding.
+
+## Alternatives considered
+- **Always-on OTLP exporter requiring a collector**: rejected — would make
+  local dev and any environment without a collector fail hard or add
+  latency/timeouts trying to reach one.
+- **Per-service ActivitySource/Meter instances**: rejected in favor of one
+  centralized `FuchsTelemetry` — avoids scattered instrument names and
+  duplicate registration boilerplate in `Program.cs`.