feat(L4-L5): KI-Steuerung + XRechnung-Format-Layer (EN16931/CII)

L5 Format-Layer (User-Klaerung: Verkaufsmodul spaeter, Format JETZT):
- einvoice.py: EN16931/XRechnung CII-XML-Generator (ElementTree, XML-Escaping gratis), Pflichtfeld-Validierung mit BT/BG-Codes, Decimal-kommerzielles Rounding, Header-Tax-Breakdown pro VAT-Satz, Profile en16931|xrechnung (XRechnung 3.0)
- POST /einvoice/render (inline->XML), /einvoice/validate (422 mit BT-Fehlliste), /einvoice/render-for (Contract-Resolver einvoice_data() — Andockpunkt Verkaufsmodul, 404 no_data_source ohne Beitrag)

L4 KI-Steuerung:
- POST /documents/suggest: Natuerliche Sprache -> Block-Komposition via zentralem llm_complete (Cost-Tracking, Tenant-Budget), Registry-Sanitizing (ungueltige KI-Bloecke gefiltert, IDs serverseitig), Code-Fence-Stripping, 502 ai_unavailable/invalid_ai_response
- Frontend: KI-Vorschlag-Panel im PrintTemplateEditor (Sparkles-Icon, Prompt-Textarea, Bloecke werden angehaengt), i18n de/en

TDD: Rot 25 failed -> Gruen 25/25 (Validierung, XML-Struktur/Escaping/Summen, Contract-Mocks, API 200/422/403/404, Suggest Mock-LLM/Fence/502). tsc exit 0, Build OK, ruff clean. Doku: api-documentation.md, plugin-development-guide.md (einvoice_data-Contract), PROGRESS.md

app/plugins/builtins/report_generator/schemas.py

@@ -162,3 +162,78 @@ class DocumentAssetResponse(BaseModel):
     size_bytes: int
     data_url: str | None = None
     created_at: datetime | None = None
+
+
+# ─── E-Invoice (EN16931/XRechnung, Phase L5) ────────────────────────────────
+
+
+class EInvoiceAddress(BaseModel):
+    """Postal address (BT-50..53 seller, BT-65..68 buyer)."""
+
+    street: str | None = None
+    postal_code: str | None = None
+    city: str | None = None
+    country: str | None = None
+
+
+class EInvoiceLineItem(BaseModel):
+    """Invoice line (BG-25). ``line_net_amount`` wins over qty*price."""
+
+    name: str = ""
+    quantity: float = 1.0
+    unit: str = "HUR"
+    unit_net_price: float = 0.0
+    vat_rate: float = 0.0
+    line_net_amount: float | None = None
+
+
+class EInvoiceRenderRequest(BaseModel):
+    """Inline invoice data — field-level semantics validated by
+    ``einvoice.validate_einvoice_data`` (BT/BG business terms, 422)."""
+
+    invoice_number: str = ""
+    issue_date: str = ""
+    type_code: str = "380"
+    currency: str = "EUR"
+    due_date: str | None = None
+    delivery_date: str | None = None
+    buyer_name: str = ""
+    buyer_reference: str | None = None
+    buyer_address: EInvoiceAddress | None = None
+    seller_name: str = ""
+    seller_vat_id: str | None = None
+    seller_tax_id: str | None = None
+    seller_address: EInvoiceAddress | None = None
+    payment_means_code: str | None = None
+    payment_terms_text: str | None = None
+    note: str | None = None
+    line_items: list[EInvoiceLineItem] = Field(default_factory=list)
+    profile: str = Field("en16931", pattern="^(en16931|xrechnung)$")
+
+
+class EInvoiceRenderForRequest(BaseModel):
+    """Render an e-invoice for an entity via the ``einvoice_data()``
+    contract hook (future sales module docking point)."""
+
+    entity_type: str = Field(..., min_length=1, max_length=100)
+    entity_id: str = Field(..., min_length=1)
+
+
+class EInvoiceValidationResponse(BaseModel):
+    valid: bool
+    missing: list[str] = Field(default_factory=list)
+
+
+# ─── AI block suggestion (Phase L4) ──────────────────────────────────────────
+
+
+class DocumentSuggestRequest(BaseModel):
+    """Natural-language block composition request for the template editor."""
+
+    prompt: str = Field(..., min_length=1, max_length=2000)
+    entity_type: str | None = Field(None, max_length=100)
+
+
+class DocumentSuggestResponse(BaseModel):
+    blocks: list[dict]
+    notes: str = ""