Control roles in the journal (books.assign_role, books.roles); the MCP reloads wanderbooks.toml on change and reports settings problems (books.settings, digest); new writes a full commented wanderbooks.toml

- core: ControlAccount keys, Ledger::assign_role/check_assign_role/role_account (rules.md B-23): one account per role, of the role's type, balance sheet roles move only when empty; invoices, bills, payroll, remittance, and closes post to the assigned account; an assigned role frees its default code for renumbering
- store: role.assigned journaled and replayed (strict account_id)
- mcp: settings.rs reloads by content at the start of each request, keeps the last good settings on a broken edit; books.settings with chart problems; digest settings_problems; instructions say when to edit the toml
- viewer: journal text for role.assigned
- cli: full example wanderbooks.toml, tested to load with every example uncommented
- tests: spec_roles.rs (25, spec-blind), store roles.rs (6), MCP reload/problems/roles, settings unit tests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

crates/ledger-core/src/lib.rs

@@ -52,7 +52,7 @@ pub use form1099::{Form1099, Vendor1099Line, Vendor1099Report, vendor_1099_repor
 pub use journal::{EntryId, EntryStatus, JournalEntry, JournalLine};
 pub use ledger::{
     ControlAccount, GENERAL_EXPENSES, Ledger, PAYABLES, PAYROLL, RECEIVABLES, RETAINED_EARNINGS,
-    REVENUE, ReconciliationReport, UnclearedLine,
+    REVENUE, ReconciliationReport, UnclearedLine, control_account, control_accounts,
 };
 pub use money::{Currency, Money};
 pub use payouts::{Payout, PayoutAdjustment, PayoutLine, PayoutTotals, payout_plan};