Sicherheit + Tests + A11y, SW by-v1118

PYDANTIC max_length (38 Routen, ~400 Field-Constraints):
Schützt vor DoS durch Riesen-Payloads (10MB Thread-Titel etc.).
Pragmatische Limits:
- Titel/Name: 200 · Beschreibung/Body: 10000 · Notiz: 5000
- Email: 254 (RFC 5321) · URL: 500 · Slug/Kategorie: 100
- Hund-Name/Rasse: 80 · Hund-Bio: 2000

Top-betroffen: forum.py, diary.py, health.py, dogs.py, expenses.py,
notes.py, auth.py, profile.py. Manuelle len()-Checks in profile,
chat, ki entfernt (jetzt durch Field abgedeckt).

PYTEST COVERAGE (+19 Tests, 37 grün + 1 xfail):
- test_security.py: require_owner (Places GET/PATCH/DELETE mit
  Fremduser → 403), JWT-Blacklist (Logout invalidiert Token),
  Login-Lockout (5 Fehlversuche → 429 + Retry-After Header)
- test_race.py: Invoice-Counter (20 parallele Threads, alle unique),
  Founder-Number (atomare Vergabe, voll bei 100)
- test_validation.py: Forum-Titel 30k Zeichen → 422, Diary-Text
  50k → 422 (verifiziert Pydantic max_length-Sweep)

A11Y (Tap-Targets ≥44×44 + Dark-Mode-Kontrast):
- #header-user-btn 36→44px, .header-back 40→44, .header-menu-btn 40→44
- dog-profile Wrapped-Slider Prev/Next 40→44
- forum-Lightbox Close 40→44
- --c-text-muted Light: #B0A090 (2.37:1 FAIL) → #7F6B58 (4.74:1 PASS)
- --c-text-muted Dark:  #806A58 (3.58:1 FAIL) → #A08878 (5.46:1 PASS)
- Branding-Farben unangetastet

backend/routes/invoices.py

@@ -6,7 +6,7 @@ from datetime import datetime
 from typing import Optional, List
 from fastapi import APIRouter, Depends, HTTPException
 from fastapi.responses import Response
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 from database import db
 from auth import require_admin
 import mailer
@@ -19,30 +19,30 @@ logger = logging.getLogger(__name__)
 # Schemas
 # ------------------------------------------------------------------
 class InvoiceItem(BaseModel):
-    description: str
-    quantity: float = 1.0
+    description: str   = Field(..., max_length=500)
+    quantity: float    = 1.0
     unit_price: float
 
 
 class InvoiceCreate(BaseModel):
     user_id: Optional[int] = None
-    recipient_name: str
-    recipient_email: str
-    recipient_address: Optional[str] = None
+    recipient_name: str    = Field(..., max_length=200)
+    recipient_email: str   = Field(..., max_length=254)
+    recipient_address: Optional[str] = Field(None, max_length=500)
     items: List[InvoiceItem]
     discount_pct: Optional[float] = 0.0
-    service_period: Optional[str] = None
-    notes: Optional[str] = None
+    service_period: Optional[str] = Field(None, max_length=200)
+    notes: Optional[str]   = Field(None, max_length=5000)
 
 
 class PayBody(BaseModel):
-    paid_at: str
+    paid_at: str        = Field(..., max_length=32)
     paid_amount: float
-    notes: Optional[str] = None
+    notes: Optional[str] = Field(None, max_length=2000)
 
 
 class CancelBody(BaseModel):
-    reason: str
+    reason: str = Field(..., min_length=3, max_length=1000)
 
 
 # ------------------------------------------------------------------