feat(package): one attention engine over PackageBooks (U0b)

Needs attention was computed by the viewer alone, while books.start
hand-picked a handful of next steps. The human's list and the agent's
could disagree, and a new item had to be written twice (or, as
books.start showed, not at all).

Move the engine to ledger-package over PackageBooks: one function,
find/find_with(books, today, settings, integrity), reads the ledger, the
journal's event types (an entry's origin), the attachments and their
links, the statements, the reconciliations, and the database check. The
viewer's attention module now only maps Target to Route; books.start
turns the same items into its next steps (why = the item's title, top 12),
so the list the human sees and the steps the agent gets cannot drift.

PackageBooks gains settings, journal, statements, reconciliations and
disk_check, implemented for Store and Snapshot, so both views answer
alike. The W-9, reconciliation and 1099 predicates move beside the items
to keep one copy. ledger-package gains ledger-config and serde_json (the
receipt policy and the tool arguments the items carry).

Tests: view_model.rs and spec_kept.rs pass unchanged; the new
attention_parity.rs compares the viewer and books.start item for item on
the demo books and on a book written entry by entry. just check green.

docs/parity.md

@@ -63,6 +63,16 @@ D-46); no file with a full TIN is filed into the books (B-26); the agent is
 told the rules in force in a short connect text and a handbook, and no
 agent text points at the books' files, git or the repo.
 
+## U0b: one attention engine (D-53, 2026-10-26)
+
+No semantic feature changed, so no status moved and the floor stands (10
+done). Needs attention used to be computed by the viewer alone; it now
+lives in `ledger-package::attention`, over `PackageBooks`, and both the
+viewer and `books.start` read it (the same items, the same prompts), so the
+list the human sees and the next steps the agent gets cannot drift. The
+parity test `the_viewer_and_books_start_see_the_same_attention` compares
+them item for item on the demo books and on a book written entry by entry.
+
 ## Capability parity (AI-first phase)
 
 Semantic parity (above) is about *correctness*: the engine computes the