fix(accounting): tax-report storno totals + hours-line date on Postgres

Two pre-existing HIGH bugs surfaced by the codebase audit (accounting surface):

- taxReportService: income totals excluded only `status='cancelled'`, never
  `kind='storno'`. A Storno (status='sent', amounts stored negative) netted into
  the totals on top of the already-excluded cancelled original → double-subtract,
  so a cancel-and-reissue read as 0 income instead of the reissued amount.
  Now exclude storno rows from grandTotal*/byRate (kept visible in the row list).
  Regression test reproduces the real cancel→storno→reissue 3-row flow.
- customerHoursService.buildLineItemFromEntry: `String(entry.entry_date).slice(0,10)`
  on a `date` column → Postgres returns a JS Date, baking "Wed Apr 06" into the
  invoice line + PDF (SQLite returns the bare string, so SQLite-only tests pass).
  Normalise via the Date branch like every other date read.

backend/src/services/customerHoursService.js

@@ -127,9 +127,14 @@ function isEntryLocked(entry, invoice) {
  */
 function buildLineItemFromEntry(entry, rateMinor) {
   const hours = (entry.duration_minutes / 60).toFixed(2);
-  // ISO date input is already YYYY-MM-DD; admin's locale formatting
-  // happens at PDF render time, so keep the entry description portable.
-  const datePart = String(entry.entry_date).slice(0, 10);
+  // Keep the entry description portable (admin's locale formatting happens at
+  // PDF render time). `entry_date` is a `date` column: Postgres hands it back as
+  // a JS Date, SQLite as a 'YYYY-MM-DD' string — so `String(dateObj).slice(0,10)`
+  // would bake "Wed Apr 06" into the invoice line on PG. Normalise via the Date
+  // branch (see feedback_pg_date_columns_serialize).
+  const datePart = entry.entry_date instanceof Date
+    ? entry.entry_date.toISOString().slice(0, 10)
+    : String(entry.entry_date).slice(0, 10);
   const note = (entry.description || '').trim();
   const description = `${datePart} ${entry.start_time}–${entry.end_time} (${hours}h)${note ? ': ' + note : ''}`;
   const qty = Number(hours);

backend/src/services/taxReportService.js

@@ -433,9 +433,15 @@ async function getTaxReport({ from, to, currency, includeCosts = true } = {}) {
     const rows = dbRows.map((r) => {
       const reported = computeReportedAmounts(r);
       const isCancelled = r.status === 'cancelled';
-      if (isCancelled) {
-        cancelledCount += 1;
-      } else {
+      if (isCancelled) cancelledCount += 1;
+      // Exclude BOTH the cancelled original AND its negative Storno row from the
+      // totals. Both stay visible in the row list for the gap-free audit trail,
+      // but a Storno (kind='storno', status='sent', amounts stored negative)
+      // would otherwise double-subtract: the cancelled original is already
+      // netted out by exclusion, so adding the negative storno on top deducts
+      // the revenue a second time — making a cancel-and-reissue read as 0 income
+      // instead of the reissued amount. See feedback_storno_filter_everywhere.
+      if (!isCancelled && r.kind !== 'storno') {
         grandTotalNet += reported.netMinor;
         grandTotalVat += reported.vatMinor;
         grandTotal    += reported.totalMinor;