Add unit tests for Fuchs_DataService and related components

- Introduced comprehensive unit tests for the Fuchs_DataService library, covering DATEV header formatting, CSV/XML generation, and FdsMfrClient construction.
- Implemented tests for FdsMfr.UpdateNeed parsing and FdsShared utility helpers, ensuring correct functionality and stability.
- Added tests for FdsConfig and FdsMfrClient to validate configuration resolution and client construction.

Document decisions on backend-authoritative invoice and reminder handling

- Created ADR 0008 to clarify that all invoice types and reminder stages are backend-authoritative during drafting and previewing.
- Established that all calculations and settings must be processed server-side, ensuring consistency between online editor and PDF outputs.

Define irreversible mutations for set-price modes in invoices

- Documented ADR 0009 to specify that the "Set mit Preis" and "Nur Set mit Preis" operations are irreversible mutations affecting service request blocks.
- Clarified that these operations are not display toggles but actual data changes, ensuring clear expectations for invoice handling.

Transition MFR ERP sync to in-process execution within the web app

- Created ADR 0010 to outline the migration of Fuchs_DataService from a standalone service to an in-process library within the Fuchs web application.
- Updated configuration and logging management to be handled by the host application, streamlining the sync process.

Add publish profile and periodic hosted service for job scheduling

- Introduced a publish profile for deployment to a specified folder.
- Implemented PeriodicHostedService to manage multiple independent jobs, including the MFR ERP sync, with configurable execution intervals.

Add dotnet-tools.json for EF Core CLI tools

- Included dotnet-tools.json to manage the version of dotnet-ef for Entity Framework Core migrations and commands.

Fuchs/Docs/INVOICE_LIFECYCLE.md

@@ -94,8 +94,10 @@ payload; see `EVAL_live_invoice_editing.md` for the rationale.
   location/period (inline edit fields, `fm(...)` helper in `fis.inv_shared.js`).
 - **§13b reverse-charge** toggle (`$inv.sp13b`) — suppresses VAT lines/columns.
 - **Set-pricing display mode** (`$inv.ssetmode` / `setSetmode`) — `SetPrice`
-  (default) / `ItemPrices` / `SetOnly`; see `INVOICE_SET_PRICING.md`. Purely
-  presentational — totals never change.
+  (default) / `SetOnly`; see `INVOICE_SET_PRICING.md`. Purely presentational
+  while the set header itself has no own price; once a set is converted via
+  the item switch (`item.setprice`), the conversion is one-way and totals
+  recompute from that point on.
 - **Contact person** for the invoice (`$inv.sctp`, stored in `CustomValues`).
 
 All of this recalculates client-side totals live via the `fds.inv` event
@@ -122,7 +124,7 @@ On the server, `RegisterInvoiceAsync` (in `InvoiceService`) turns the posted
 JSON into SQL parameters and calls, in one batch:
 - **New invoice**: `fds__createInvoice` (allocates the `Id`, returns a fresh
   row) → `fds__createInvoice_Details` (service net/VAT + `InvoiceOptions`,
-  e.g. `setmode:itemprices`, `§13b`).
+  e.g. `setmode:setonly`, `§13b`).
 - **Existing draft**: `fds__setInvoice` (same parameter set, updates in place)
   → `fds__createInvoice_Details` again.