P2 slice 6: the viewer

`wanderbooks gui [BOOK]` finds the data root, reads settings from the
journal, the vault of the book, presence through ops/, Save a copy /
Open on every document, Save the W-9, the Export menu, and colour
schemes. One builder for the CPA package and the 1099 worksheet
(ledger-package), shared by the server and the viewer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-gui/tests/tin_copy.rs

@@ -73,7 +73,6 @@ fn fixture(tag: &str) -> Fixture {
 fn load(f: &Fixture, key: Option<&Path>) -> Books {
     let mut b = data::load_once(&Source {
         data_dir: f.books.join("books-data"),
-        books_toml: None,
         today: Some(chrono::NaiveDate::from_ymd_opt(2026, 10, 16).unwrap()),
     })
     .unwrap();