test(ledger): reach full backend coverage

[roncodes]

Summary

• Add deterministic Pest coverage across Ledger services, gateways, controllers, listeners, models, observers, resources, routes, provider wiring, notifications, and console commands.
• Cover success, failure, validation, API contract, persistence, webhook, external-provider, and accounting lifecycle behavior without live external dependencies.
• Correct small production issues exposed by behavior tests, including controller return contracts, chunked transaction backfill, webhook/listener query paths, and testability seams for seeders and command environment reads.
• Improve the isolated package harness without adding Orchestra, and derive class coverage from per-class statement metrics when Clover omits aggregate covered-class counts.

Coverage

• Lines: 100.00% (6655/6655)
• Methods: 100.00% (548/548)
• Classes: 100.00% (73/73)
• Raw Clover uncovered statements: 0

Validation

• composer test:unit — 302 passed
• XDEBUG_MODE=coverage composer coverage:baseline
• composer coverage:summary
• Raw coverage/clover.xml uncovered-statement scan
• composer lint
• git diff --check

Covered areas

• Payment gateway contracts and Stripe, QPay, and GNU Taler success and failure paths
• Invoice, wallet, payment, ledger, revenue lifecycle, refund verification, and settlement services
• Internal, public, accounting, gateway, reporting, search, settings, wallet, and webhook controllers
• Payment/refund listeners, model lifecycle and contracts, observers, notifications, API resources, filters, and route registration
• Provisioning, repair, overdue invoice, direction backfill, Taler refund/settlement verification, and sandbox commands

Narrow coverage exclusions

• Purchase-rate observer fallback when the required Fleet-Ops API package class is absent; the package is a required Composer dependency in supported runtime installations.
• Revenue-lifecycle repair warning when the required Fleet-Ops order class is absent; the same required dependency contract applies.
• Service-provider guard when the required core template rendering service is absent; supported installations always provide it.
• Invoice resource generic fallback when resource lookup returns null; core resource lookup always returns a registered resource or FleetbaseResource.

Each exclusion is limited to the unreachable defensive branch and documented inline.

[roncodes]

CI status: the backend/package build and all CodeQL checks pass. The remaining repository-wide build failure is inherited from parent PR #14 and occurs before backend validation in JavaScript lint: addon/components/customer-taler-refund.js:63 and addon/components/gateway/form.js:85 require Prettier-only parenthesis removal. Those files are not part of this stacked PR diff and remain unchanged to preserve the backend-only scope.