feat(mcp): books.journal_history, the journal in words (P5)

Agent reason: an agent traces a figure back to what produced it by reading
the journal, but it must never read the file. books.journal_history is the
one way: each line in order with its seq, time, type, a sentence saying what
it did to what, its subject and the entry it belongs to, filtered by
after_seq, type (exact, or a group like entry.) and subject (entry:12,
invoice:3, bill:3, account:10, party:5, asset:2), paged with more, with the
torn tails set aside on open listed beside them. It reads the verified
journal through read_journal_and_format, so a damaged chain is an error, not
a story.

The sentences come from ledger-store's describe.rs, which quotes only
identifiers, dates, amounts and the short names a person typed: never a
setting's value (settings.set names its keys) and never a full TIN (masked,
B-26). Every event type the store writes has a sentence (tested against
EVENT_TYPES). The tool is read-only (books:read); the books://journal/{seq}
and books://entries/{id} resources read through it.

Departure from the plan: the viewer's own sentences (its describe arms in
ledger-gui, which carry icons, routes and today's party and account names)
stay where they are; moving a thousand lines of egui text behind a
formatting trait was not worth the risk to the viewer's tests, so the server
has the shared describer and the viewer keeps its own.

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

crates/ledger-mcp/src/scopes.rs

@@ -56,7 +56,7 @@ const C: Needs = PostWhenConfirmed;
 const K: Needs = PostForApprovalRules;
 
 /// Every tool and what it needs (INVARIANT 1).
-pub const TABLE: [(&str, Needs); 133] = [
+pub const TABLE: [(&str, Needs); 134] = [
     ("books.handbook", R),
     ("books.start", R),
     // Settings are committed at once: the settings commit of the plan.
@@ -200,6 +200,8 @@ pub const TABLE: [(&str, Needs); 133] = [
     ("books.list_drafts", R),
     ("books.set_draft_state", W),
     ("books.discard_draft", C),
+    // P5
+    ("books.journal_history", R),
     ("books.preview_entry", R),
 ];