feat: implement CSV import wizard with folder-based source detection
Full import pipeline: Rust backend (6 Tauri commands for folder scanning,
file reading, encoding detection, hashing, folder picker), TypeScript
services (DB, import sources, transactions, auto-categorization, user
preferences), utility parsers (French amounts, multi-format dates),
12 React components forming a 7-step wizard (source list, config,
column mapping, preview, duplicate detection, import, report), and
i18n support (FR/EN, ~60 keys each).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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