feat: add BO Produkt and degrade BO Tarif to COM Tarif (draft for AG)

[lord-haffi]

Draft — first of two PRs implementing the new BO Produkt / BO Vertrag model from the AG HackMD spec. PR 2 (BO Vertrag rework) is intentionally separate and will reference Produkt.

Changes

• New BO Produkt (standalone/unreferenced for now) with the tariff's identifying/marketing fields promoted up: bezeichnung, beschreibung, sparte, anbieter, zeitraum_vermarktung, zeitraum_belieferbarkeit, vertragskonditionen, website, kundentypen, plus new produkttyp and tarif.
• BO Tarif → COM Tarif (bo/tarif.py → com/tarif.py, base Tarifinfo → COM), keeping only the pricing-specific fields (regionspreise, dynamische_preisposition_quelle, energiemix, tariftyp, tarifmerkmale, registeranzahl, preisgarantie, berechnungsparameter, tarifeinschraenkung).
• New Produkttyp enum (TARIFPRODUKT); Kundentyp.INDUSTRIE; BoTyp.PRODUKT added, BoTyp.TARIF removed; ComTyp.TARIF added.

Verification

• pytest: 111 passed
• pylint src/bo4e: 10.00/10 · mypy: clean (286 files)
• JSON-schema generate + validate: both pass (adds bo/Produkt.json, com/Tarif.json, enum/Produkttyp.json; removes bo/Tarif.json)

Open questions for the AG

1. COM Tarif no longer inherits Tarifinfo (which stays a BO alongside Tarifkosten/Tarifpreisblatt). Field duplication was accepted; is the hierarchy split acceptable, or should Tarifinfo be revisited?
2. Several former BO Tarif fields were required (no default); all moved/new fields are now Optional = None. Please confirm this required→optional relaxation.
3. BoTyp.TARIF removed outright (vs. keeping a deprecated alias).
4. COM Tarif.regionspreise docstring references a dynamischePreisposition field that does not exist on the class (pre-existing) — reconcile with dynamic-tariff modelling, likely in a later PR.
5. vertragskonditionen intentionally duplicated on Produkt (and later Vertrag) — overridable at contract time, per spec.

Out of scope (→ PR 2)

Bündelvertrag removal, Vertragsstatus reduction, COM Unterschrift removal, Vertragsteil → Lokationszuordnung reference, and wiring Produkt into Vertrag.