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/read_only.rs

@@ -112,7 +112,6 @@ fn the_viewer_never_writes_into_the_books() {
     ledger_gui::demo::build(&dir, today).unwrap();
     let source = Source {
         data_dir: dir.join("books-data"),
-        books_toml: Some(dir.join("wanderbooks.toml")),
         today: Some(today),
     };
     set_read_only(&dir, true);