feat: UI polish, lint fixes, onboarding redesign, help page expansion, and test improvements

Broad update across dashboard pages, components, extensions, and lib code. Includes ESLint config additions, onboarding flow redesign, settings page refactor, help page content expansion, dead code removal, and test mock fixes. Adds dev docs and public assets.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/api/transactions/[id]/match-supplier-invoice/route.ts

@@ -1,6 +1,5 @@
 import { createClient } from '@/lib/supabase/server'
 import { NextResponse } from 'next/server'
-import { findFiscalPeriod } from '@/lib/bookkeeping/engine'
 import {
   createSupplierInvoicePaymentEntry,
   createSupplierInvoiceCashEntry,
@@ -9,41 +8,6 @@ import { validateBody } from '@/lib/api/validate'
 import { MatchSupplierInvoiceSchema } from '@/lib/api/schemas'
 import type { SupplierInvoice, SupplierInvoiceItem } from '@/types'
 
-/**
- * Ensure a fiscal period exists for the given date
- */
-async function ensureFiscalPeriod(
-  supabase: Awaited<ReturnType<typeof createClient>>,
-  userId: string,
-  date: string
-): Promise<string | null> {
-  const existingPeriodId = await findFiscalPeriod(supabase, userId, date)
-  if (existingPeriodId) return existingPeriodId
-
-  const transactionDate = new Date(date)
-  const year = transactionDate.getFullYear()
-
-  const { data, error } = await supabase
-    .from('fiscal_periods')
-    .upsert({
-      user_id: userId,
-      name: `Räkenskapsår ${year}`,
-      period_start: `${year}-01-01`,
-      period_end: `${year}-12-31`,
-    }, {
-      onConflict: 'user_id,period_start,period_end',
-    })
-    .select('id')
-    .single()
-
-  if (error) {
-    console.error('Failed to create fiscal period:', error)
-    return null
-  }
-
-  return data?.id || null
-}
-
 /**
  * POST /api/transactions/[id]/match-supplier-invoice
  *

app/api/transactions/suggest-categories/route.ts

@@ -1,7 +1,7 @@
 import { createClient } from '@/lib/supabase/server'
 import { NextResponse } from 'next/server'
 import { getSuggestedCategories, mergeAiSuggestions, getSuggestedTemplates, type SuggestedCategory, type SuggestedTemplate } from '@/lib/transactions/category-suggestions'
-import type { Transaction, TransactionCategory, EntityType } from '@/types'
+import type { Transaction, EntityType } from '@/types'
 
 /**
  * POST /api/transactions/suggest-categories