feat: import parts and stock from Huggett invoice PDFs

The parts page's import menu gains "Huggett-Rechnung (PDF)": drop or
pick an invoice, the backend parses it (local LLM with deterministic
fallback), and a wide review dialog shows every position — matched
parts become stock entries, unknown part numbers become new parts
enriched from the BMWBike catalog (name, image, fitment), each row with
editable quantity, total price and its own storage location plus a
set-all convenience. Nothing is written until the import is confirmed;
committed stock carries the invoice number in its notes, which feeds
the already-imported warning on re-upload. Modal gains a "lg" size for
the review layout.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PQBG6D5kahSu9frv13XQ4W

Author: mightea