feat(mcp): books.documents and books.document (P4b S2, read tools)

books.documents lists invoices or bills, due date first, with what each
still owes and its status, all derived from its ledger lines that stand
(B-38): status open (default), overdue, paid, void, written_off,
overpaid or all; party and due_by narrow it (what to pay this week).
books.document shows one (ref invoice:N or bill:N) as of a day: lines
with projects, total, paid, discounted, written off, outstanding,
status, days overdue, and its timeline of every tagged ledger line, each
saying whether its entry still stands. The over-the-wire test
documents_list_and_timeline_over_the_wire covers a reversed payment;
the happy-path journey covers both output schemas.

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

crates/ledger-cli/tests/mcp_journeys.rs

@@ -125,7 +125,7 @@ fn mcp_end_to_end() {
     // Tool listing: the narrow tools; chart is read-only.
     let list = mcp.request("tools/list", json!({}));
     let tools = list["result"]["tools"].as_array().unwrap();
-    assert_eq!(tools.len(), 120, "expected 120 tools, got {}", tools.len());
+    assert_eq!(tools.len(), 122, "expected 122 tools, got {}", tools.len());
     // Files come in as tool input: books.begin_upload, never a local path.
     assert!(tools.iter().any(|t| t["name"] == "books.begin_upload"));
     assert!(!tools.iter().any(|t| t["name"] == "books.import_local_file"));