add the invoices ui over the invoiceshelf sidecar

a /invoices workspace screen replicating the parts of the invoiceshelf web ui
that are actually used: dashboard, invoices, estimates, recurring invoices,
payments, expenses, customers, items and reports.

one document editor serves invoices, estimates and recurring invoices — they
share the line-item table, the discounts, the taxes and the totals, and differ
only in a header strip. the arithmetic is a port of upstream's
use-document-calculations, rounding points included, because the server
re-validates the totals it is sent. money is integer minor units throughout and
is converted to major units at the edges only.

selection and editor state live in the url (`/invoices/:section`, `?selected=`,
`?edit=`), so the nav highlight is derived rather than held, back closes an
editor instead of leaving the screen, and a half-written form survives a reload.

sending a document is behind an explicit confirmation — it emails the customer.

built against the running 2.4.2 instance rather than the 3.0 checkout in
_references; the two differ materially. typechecked, not yet exercised in a
browser.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/apps/officer-web/App.tsx

@@ -46,6 +46,8 @@ export function App() {
             <Route path="/headscale/:section" element={<Dashboard.HeadscaleScreen />} />
             <Route path="/transmission" element={<Dashboard.TransmissionScreen />} />
             <Route path="/transmission/:section" element={<Dashboard.TransmissionScreen />} />
+            <Route path="/invoices" element={<Dashboard.InvoicesScreen />} />
+            <Route path="/invoices/:section" element={<Dashboard.InvoicesScreen />} />
             <Route path="/system-monitor" element={<Dashboard.SystemMonitorScreen />} />
             <Route path="/activity" element={<Dashboard.ActivityScreen />} />