feat(import/export): article import + register export (xlsx/csv) (#750)

* feat(import/export): article import + register export (xlsx/csv)

Add CSV/Excel import for the article register (artiklar), mirroring the
existing customer/supplier import pipeline, plus Excel + CSV export for
articles, customers and suppliers.

Import (lib/import/articles + app/api/import/articles):
- Column auto-detection tuned to Fortnox/Visma/Bokio export headers,
  Swedish-decimal price parsing, VAT snapped to {0,6,12,25}, type/unit
  normalization.
- Dedup by article number then name; 23505 soft-skip; auto-number
  backfill; revenue-account override kept only when active, otherwise
  dropped with a warning (never mutates the chart of accounts).
- New "Artiklar" flow in the /import hub.

Export (app/api/export/* + lib/export/register-export):
- Read-only xlsx (default) / csv (?format=csv, UTF-8 BOM) downloads.
- Headers chosen so files round-trip back through the importer.
- "Exportera" menu added to the articles, customers and suppliers pages.

Refs #746. Direct Fortnox/Visma API article fetch tracked in #749.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(import/export): address PR review — lint ratchet + export hardening

- xlsx-export: keep `SheetSpec<any>` on the eslint-disabled line (fixes the
  core-only lint ratchet regression: no-explicit-any 16 -> 15) and define
  UTF8_BOM as an explicit `` escape instead of a raw BOM character.
- export routes (articles/customers/suppliers): move the data queries inside
  the try/catch, add `Cache-Control: no-store`, and emit a `register exported`
  audit log line (entity, format, rowCount).
- articles parse route: validate `column_overrides` against a Zod schema before
  trusting it to drive the parser.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(import): drop öre-round pattern on article column-detector confidence

The confidence score is a 0-1 heuristic, not money, and is only compared
against the 0.8 skip-mapping threshold. Removing the Math.round(x*100)/100
form clears the core-only antipattern ratchet (naive-ore-round 660 -> 659).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* feat(import): flag adjusted VAT rows in the article import edit step

Surface VAT snapping/defaulting per row, not just as a file-level warning:
the parser sets `vat_rate_adjusted`, the edit step highlights those rows'
VAT selector and shows a count banner, and confirming a rate clears the flag.
Addresses the Swedish-compliance review note that silent snapping could
otherwise store a wrong VAT rate at scale.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

components/import/RegisterResultStep.tsx

@@ -12,10 +12,12 @@ export type RegisterResult = {
   skipped: number
   failed: number
   errors: { row_index: number; name: string; reason: string }[]
+  /** Non-fatal notes (e.g. dropped revenue-account overrides on article import). */
+  warnings?: string[]
 }
 
 interface RegisterResultStepProps {
-  entity: 'customers' | 'suppliers'
+  entity: 'customers' | 'suppliers' | 'articles'
   result: RegisterResult
   onNewImport: () => void
 }
@@ -33,6 +35,12 @@ const ENTITY_COPY = {
     listLabel: 'Visa alla leverantörer',
     listHref: '/suppliers',
   },
+  articles: {
+    successTitle: 'Artiklar importerade',
+    failTitle: 'Importen misslyckades',
+    listLabel: 'Visa alla artiklar',
+    listHref: '/articles',
+  },
 } as const
 
 export default function RegisterResultStep({
@@ -94,6 +102,23 @@ export default function RegisterResultStep({
           </div>
         )}
 
+        {/* Warnings (non-fatal — e.g. dropped revenue-account overrides) */}
+        {result.warnings && result.warnings.length > 0 && (
+          <div className="space-y-2">
+            <h4 className="text-sm font-medium">Att notera</h4>
+            <div className="rounded-lg border border-warning/30 bg-warning/5 px-4 py-3">
+              <ul className="space-y-1 text-sm text-muted-foreground">
+                {result.warnings.map((w, i) => (
+                  <li key={i} className="flex items-start gap-2">
+                    <AlertTriangle className="h-3.5 w-3.5 text-warning mt-0.5 shrink-0" />
+                    <span>{w}</span>
+                  </li>
+                ))}
+              </ul>
+            </div>
+          </div>
+        )}
+
         <div className="flex flex-wrap gap-3">
           <Button asChild>
             <Link href={copy.listHref}>