fix: trial balance 1000-row limit and rename /nyckeltal to /kpi (#79)

* fix: trial balance silently truncated at 1000 entries, rename /nyckeltal to /kpi

Trial balance bug:
- The old implementation fetched journal entry IDs (capped at 1000 by
  Supabase default limit), then queried lines via .in(entryIds) which
  also hit URL length limits with large arrays of UUIDs.
- SIE imports create thousands of entries → KPIs showed zero.
- Replaced with a single joined query (journal_entry_lines → journal_entries)
  using fetchAllRows() pagination. No row limit, no URL length issue.
- Removed the non-existent generate_trial_balance RPC call.

Page rename:
- /nyckeltal → /kpi (CLAUDE.md: all code in English)
- Nav label stays "Nyckeltal" (user-facing Swedish UI)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: select filtered columns in joined query, rename component, add redirect

- Select user_id/fiscal_period_id/status from journal_entries!inner()
  so PostgREST applies embedded filters reliably (defense in depth)
- Rename NyckeltalPage → KpiPage per English code convention
- Add permanent /nyckeltal → /kpi redirect for existing bookmarks

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

components/dashboard/DashboardNav.tsx

@@ -55,7 +55,7 @@ interface NavItem {
 // All nav items for sidebar and mobile drawer
 const navItems: NavItem[] = [
   { href: '/', label: 'Översikt', icon: LayoutDashboard, group: 'main' },
-  { href: '/nyckeltal', label: 'Nyckeltal', icon: TrendingUp, group: 'main' },
+  { href: '/kpi', label: 'Nyckeltal', icon: TrendingUp, group: 'main' },
   { href: '/deadlines', label: 'Deadlines', icon: Calendar, group: 'main' },
   { href: '/invoices', label: 'Fakturor', icon: Receipt, group: 'finans' },
   { href: '/customers', label: 'Kunder', icon: Users, group: 'finans' },