Key the set-price menu modes on the set instead of the service-request block (ADR 0019)

"Set mit Preis" / "Nur Set mit Preis" collapsed every block into an inserted
"Gesamtumfang pauschal" row, nulled/removed all lines and cleared the user-defined
set structure. Both modes now convert every still-unconverted top-level set:
the set line takes the sum of its subtree, its members render without a price
(setprice) or are removed from itm + items (setonly); lines outside a set stay
individually priced and several sets stay separate lines. Nested sets are priced
once via their top-level set. One conversion primitive (ConvertSetHeader) now
backs all three triggers; item.setprice is a no-op on an already-converted set
(a repeated delta used to reset the set price to 0). The header's price_net is
mirrored too (flat PDF path unit price), and Build treats a null total_net as
"no price" like the flat path. The editor checks for a set before offering the
modes and the menu entry stays available for sets added later.

ADR 0009 is superseded by 0019; INVOICE_SET_PRICING.md rewritten accordingly.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Fuchs/Docs/Decisions/0009-block-setprice-modes-are-irreversible-mutations.md

@@ -1,5 +1,5 @@
 ---
-status: Accepted
+status: Superseded
 date: 2026-07-14
 applyTo:
   - "Fuchs/code/InvoiceSetPricing.cs"
@@ -10,7 +10,7 @@ applyTo:
   - "Fuchs/code/FuchsPdf.cs"
   - "Fuchs/js/intranet/**"
   - "Fuchs/Docs/INVOICE_SET_PRICING.md"
-supersededBy: ""
+supersededBy: "0019-set-price-modes-are-keyed-on-the-set.md"
 ---
 
 # 0009 — The two menu set-price modes are per-service-request-block, irreversible cache mutations that insert a dedicated set row