merge: P4b S7, bad debts (branch S7, 4b4fecb9)

The fourth of the paused branches: Ledger::write_off and the bad_debts
control role, invoice.written_off with its evidence filed in the same
store call, books.write_off_invoice, the write-off on the timeline and
in Needs attention, Lean writeOff_within_bounds, rules.md B-41 and the
bookspec examples. Twenty-eight files conflicted with the S4.4, S5 and
S6 merges; resolved as plan 8.0.2 says, keeping both sides' appends with
their seams restored, and: the scope table at 125; S7's law numbered 37;
B-41 placed before B-42; the handbook's step 4 and recovery procedures
folded into the one invoices-and-bills section; S7's wire tests in their
own module with the confirm S4.4's contract needs; S7's copy of the
payment steps dropped (S6 replaced them with Ledger::settle) and its
write-off journaled through S6's journal_auto_lines; in the old-books
fixture S7's hand-written write-off moved to a second invoice, since
S6's hand-written payment settles invoice 1 in full.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

docs/architecture.md

@@ -184,6 +184,9 @@ groups are:
 - `parties` — parties, vendors, customers, roles, W-9s, the TIN vault,
   1099s, entry parties;
 - `attachments` — receipts, filed documents, and their links;
+- `write_offs` — `books.write_off_invoice`, the bad debt (P4b S7; rules.md
+  B-41), kept apart from `documents` so S4.4's document tools and this one
+  land in different files;
 - `settings` — the handbook, `books.settings` and the recorded FX rates
   (the module is `settings_tools`, since `crate::settings` is the live
   settings);