feat: transaction categorization UX improvements and description matching

Add journal entry preview, human-readable account names, auto-apply VAT,
fallback template suggestions, example prompts, invoice match comparison,
and batch result feedback. Also includes user-description-match extension,
describe/batch-describe API routes, improved AI categorization with multi-
suggestion support, and template embedding search.

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

supabase/migrations/20240101000041_user_description_matching.sql

@@ -0,0 +1,23 @@
+-- Migration: user_description_matching
+-- Adds source tracking, user description text, and template_id to mapping_rules
+-- to support user-description-based transaction matching.
+--
+-- Safe migration: all new columns have defaults or are nullable,
+-- so existing rows remain valid.
+
+-- 1. Add source column to track rule origin
+ALTER TABLE public.mapping_rules
+  ADD COLUMN IF NOT EXISTS source TEXT NOT NULL DEFAULT 'auto'
+  CHECK (source IN ('auto', 'user_description', 'system'));
+
+-- 2. Add user_description column to store the user's plain-language text
+ALTER TABLE public.mapping_rules
+  ADD COLUMN IF NOT EXISTS user_description TEXT;
+
+-- 3. Add template_id column to store the confirmed booking template
+ALTER TABLE public.mapping_rules
+  ADD COLUMN IF NOT EXISTS template_id TEXT;
+
+-- 4. Index for efficient upsert-on-merchant lookup by source
+CREATE INDEX IF NOT EXISTS idx_mapping_rules_user_merchant_source
+  ON public.mapping_rules (user_id, merchant_pattern, source);