refactor(mcp): the eight long tool descriptions move into the handbook (P5)

Agent reason: a tool description is read every time the tool list is, so
eight descriptions of 800 to 2,000 characters cost every session for text
only a few calls need. books.export, books.export_cpa_package,
books.import_bank_csv, books.reconcile, books.set_entry_party, books.set_w9,
books.show and books.vendor_1099 now say what the tool is for, what it
requires and where the rest is, in at most 700 characters; the rest is in
the handbook, verbatim: the CPA package's contents (cpa-handoff), the share
rules of a multi-party tag and the W-9 procedure (parties-and-tins), the
worksheet's construction (1099), the CSV import and the report list with
the IIF limits (files-in-out), the reconciliation's answer (reconciliation)
and the targets books.show opens (viewer).

tool_descriptions_fit_700_characters now pins zero and its allowance list is
deleted: no description may exceed the cap, and none is excused. The period
test keeps its sentence about omitted dates in books.export's description.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

crates/ledger-mcp/src/server_tests.rs

@@ -716,23 +716,10 @@ fn tool_text_lint() {
     }
 }
 
-/// Tool descriptions are at most 700 characters (plan I-12). The
-/// ones over it today are listed, each to be shortened in P5 when its
-/// text moves into the handbook; no new one may join them, and one
-/// that shrinks under the cap must leave the list.
+/// Tool descriptions are at most 700 characters (plan I-12); the long
+/// text lives in the handbook (P5 moved the last eight there).
 #[test]
 fn tool_descriptions_fit_700_characters() {
-    // Shorten in P5.
-    const OVER: &[&str] = &[
-        "books.export",
-        "books.export_cpa_package",
-        "books.import_bank_csv",
-        "books.reconcile",
-        "books.set_entry_party",
-        "books.set_w9",
-        "books.show",
-        "books.vendor_1099",
-    ];
     let mut over: Vec<String> = BooksServer::tool_router()
         .list_all()
         .iter()
@@ -740,7 +727,7 @@ fn tool_descriptions_fit_700_characters() {
         .map(|t| t.name.to_string())
         .collect();
     over.sort();
-    assert_eq!(over, OVER, "tool descriptions over 700 characters");
+    assert!(over.is_empty(), "tool descriptions over 700 characters: {over:?}");
 }
 
 /// The tools docs/mcp-interface.md documents: a line (or a bullet)