Docs: update ARCHITECTURE + copilot instructions, add CLAUDE.md + USER_GUIDE

- ARCHITECTURE.md: reflect the implemented DI service layer, CAMTParser,
  OpenTelemetry/observability, the ported report engine, and CAMT+MT940
  banking; mark the resolved observations.
- copilot-instructions.md: add Services/DI, dual-format banking, observability
  and testing sections; add an Instruction-Sync banner.
- CLAUDE.md (new): Claude Code project instructions mirroring the shared rules,
  plus build/test workflow notes. Both files state they must stay in sync.
- USER_GUIDE.md (new, Fuchs/Docs): end-user process guide (login, invoices,
  reminders, requests, banking incl. MT940/CAMT upload, DATEV, reports).

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

.github/copilot-instructions.md

@@ -1,5 +1,13 @@
 # Copilot Instructions
 
+> ## ⚠️ Instruction Sync
+> This file (`.github/copilot-instructions.md`) and the Claude Code instructions
+> (`/CLAUDE.md`) are **two views of the same project rules and must stay in sync**.
+> Whenever you change one, make the equivalent change in the other in the same
+> commit. `CLAUDE.md` may add tool-specific workflow notes, but the shared
+> project facts (architecture, coding standards, configuration, libraries,
+> secrets, observability) must match.
+
 ## Project Overview
 - **Fuchs Intranet** is an ASP.NET Core (.NET 10) web application — the intranet IS the entire website, served from `/`.
 - Routes: `/{fn?}/{id?}/{code?}` → `IntranetController.Index`; `/do/{fn?}/{id?}/{code?}` → `IntranetController.Do`.
@@ -31,6 +39,26 @@
 - Do not use OCMS or OCMS_sharp; use only OCORE or OCORE_web.
 - For builds failing due to SixLabors.ImageSharp requiring a license (v4.0.0+), check copilot-instructions.md for the SixLabors license key/handling info before downgrading ImageSharp.
 
+## Services & Dependency Injection
+- Business logic lives in **DI-registered services** under `Fuchs/Services/` behind interfaces; inject them into `IntranetController` (constructor injection). Do **not** reintroduce static God-classes or pass the whole controller into helpers.
+  - `IComService` (email/SMS via ProcessWeb Mailer API, attachments sent inline as base64), `IPdfService` (MigraDoc render), `IInvoiceService`, `IReminderService`, `IReportService` (SQL report engine via `FuchsVisualization`), `IWidgetService`, `IBankingService`, `IMfrClientFactory`.
+  - Lifetimes: stateless services (`IPdfService`, `IBankingService`, `IMfrClientFactory`) are singletons; request-scoped DB services (`IInvoiceService`, `IReminderService`, `IReportService`, `IWidgetService`, `IComService`) are scoped. Register in `Program.cs`.
+- `FdsInvoiceData` / `FdsReminderData` are **pure data holders** (parse + properties). Loading, persistence and PDF generation belong in the services — never `Task.Run(...).Wait()` sync-over-async.
+- Data access stays SQL-first via OCORE helpers (`getSQLDataSet_async`, `setSQLValue_async`) + stored procedures; no EF Core.
+
+## Bank statement parsing (MT940 + CAMT)
+- Two parsers feed the same banking pipeline: the external `MT940Parser` (SWIFT text) and the in-repo **`CAMTParser`** project (ISO 20022 camt.052/053/054 XML).
+- `BankingService.ParseToDatatable` **auto-detects** the format (XML → CAMT, else MT940) and maps both into the `fds__tt__bankingtransactions` schema. The `bam/up` handler and the frontend file picker accept both (`.sta/.mt940/.txt` and `.xml/.camt`).
+- `CAMTParser` is namespace-agnostic (matches elements by local name) so it handles every camt schema version. Keep both parsers' column mappings aligned when changing the banking schema.
+
+## Observability
+- Use **OpenTelemetry**. The app's instrumentation is centralised in `Fuchs/Observability/FuchsTelemetry.cs` (one `ActivitySource` + one `Meter`).
+- When adding a meaningful operation: start an activity (`FuchsTelemetry.StartActivity(...)`), record the relevant counter/histogram, and log entry/result/timing/errors via the injected `ILogger<T>`. Prefer structured logging (named placeholders), never string interpolation in log messages.
+- Tracing/metrics are always collected; OTLP export is opt-in via `Fuchs:Telemetry:OtlpEndpoint`. Don't add exporters that fail hard when no collector is present.
+
+## Testing
+- xUnit in `Fuchs.Tests`. For every service/handler change add tests covering **both** an intentionally succeeding and an intentionally failing path where feasible (use stubs/mocks; the test project has `InternalsVisibleTo`). DB-bound paths that can't be unit-tested should at least have their pure logic covered.
+
 ## Azure Key Vault — Secret Naming
 - Secret names must satisfy the pattern `^[0-9a-zA-Z-]+$` (alphanumerics and hyphens only; no underscores, dots, or spaces).
 - Hierarchy levels are separated by `--` (double hyphen), which maps to `:` in `IConfiguration`.