refactor!: one way to serve books: the stdio server is gone (D-44)

The owner (2026-10-23): "We should probably just delete the stdio path
altogether. THere's no point in that. And it sitting there unused will
just lead to bitrot. Nuke it?"

Books are served only by the books server (`wanderbooks server`),
reached by agents through the bridge (`wanderbooks mcp --book ID`),
which stays.

Removed: `wanderbooks dev-stdio`, the `ledger-mcp` binary, and
`ledger_mcp::run` (stdio and `--http` over a bare data dir), with all
that only that mode had:
- files the books make coming back inline: `HandedFile.content_base64`
  is gone, and `download` and `expires_at` are always there;
- books with no access log or backups: `books.access_log`,
  `books.backup` and `books.back_up_now` are always offered, by scope;
- the settings file read and reloaded (`legacy_files`), the vault key
  named by a file or `--vault-key-file`, and the books dir's
  key-inside-the-books and git checks (with `paths.rs`);
- `wire.rs` (the bridge frames an agent's lines itself);
- `books.settings`' file fields and `books.start`'s `settings_source`.

`BooksServer` is built one way, from `Served` (a book as the books
server serves it), in production and in the unit tests. An unknown tool
is now a protocol error (mcp-tools.md). Inline file input is unchanged.

Then the owner's three decisions (2026-10-23, the question tool):
(a) `books.import_settings` is removed entirely (118 tools): old books
come in whole by `wanderbooks books adopt`, which reads their settings
file once; ledger-config keeps its settings-file parsing only as far as
adoption uses it (`load` and the path-reading `effective_receipt_policy`
are gone), and `books.chart_template` gives its settings as
`books.set_setting` changes. (b) The viewer's loose-books-folder mode is
removed (`--data-dir`, `--books-toml`, `--vault-key-file`, the settings
file and config.json followed): it opens only books of the data root,
reading settings from the journal and the vault from the book's own
`vault/` and `keys/`. (c) `wanderbooks dev-stdio` has no stub: it is an
unknown command like any other word. Also: an upload's expiry past the
calendar is an error, never an empty string.

Tests: every suite that drove the stdio server moved to
crates/ledger-cli/tests/ and drives a real `wanderbooks server` on a
data root of its own (tests/common), handed files by their download;
mcp_stdio.rs is mcp_journeys.rs. Tests of what is gone are deleted and
listed in docs/testing.md. Docs: plan D-44 (D-18 superseded), STATUS,
testing, rules, mcp-interface, the handbook, README; justfile recipes.

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

crates/ledger-mcp/handbook/settings-and-conventions.md

@@ -11,17 +11,6 @@ The books keep their own record of how they are kept. Every agent, anywhere, rea
 - policy.require_tax_category is warn (unset: a revenue or expense account without a tax category is created, and the result and Needs attention say so) or refuse (books.add_account, books.import_chart_csv and books.set_tax_category won't leave one without; the accounts invoices, bills and payroll create are never refused, and their results name them). Before setting refuse, categorize with the human every account books.digest lists in uncategorized_accounts.
 - books.export_settings writes the settings out as a settings file (TOML), each with who decided it. It is a copy: editing it changes nothing.
 
-## Books that still read a settings file
-
-If books.settings says source "file", these books predate settings in the books and still read the settings file books.settings names. Move it in once, with the human:
-
-1. Read that file's text, whole and unedited, and pass it to books.import_settings as toml_text (and, if books.settings shows config_json_present, the receipt policy as config_json_text: {"receipt_policy": {"require_receipts_above", "receipt_required_accounts", "receipt_exempt_accounts"}} from books.settings). The import is refused unless the text is the file the server reads.
-2. Show the human the preview: every change, the notes (what isn't a books setting and where it goes), anything unknown, and the file's comments, which are not imported: record what matters in them (where a value came from, a discrepancy, something pending) as a decision, an open item or a convention.
-3. Confirm with confirmed: true, decided_by the human. The import is refused if any setting would read differently afterwards.
-4. If the file named the vault's key file ([vault] key_file), the server must already be started naming the same file, and the viewer too, or the vault won't open: tell the human before the import.
-
-From then on no file is read; books.set_setting changes settings. Until then, that file is the one local file you may edit, and books.set_setting is refused (it would drop the rest of the file).
-
 ## Conventions
 
 How this company keeps its books, as the owners decided, is recorded as conventions (books.set_convention, read with books.conventions; books.start lists them):