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/walks.py

@@ -4,7 +4,7 @@ import os, uuid
 import httpx
 from datetime import date
 from fastapi import APIRouter, Depends, HTTPException, UploadFile, File
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 from typing import Optional, List
 from database import db
 from auth import get_current_user
@@ -20,24 +20,24 @@ router = APIRouter()
 # Schemas
 # ------------------------------------------------------------------
 class WalkCreate(BaseModel):
-    titel:          str
-    datum:          str           # YYYY-MM-DD
-    uhrzeit:        str           # HH:MM
+    titel:          str           = Field(..., min_length=1, max_length=200)
+    datum:          str           = Field(..., max_length=32)        # YYYY-MM-DD
+    uhrzeit:        str           = Field(..., max_length=20)        # HH:MM
     lat:            float
     lon:            float
-    ort_name:       Optional[str] = None
+    ort_name:       Optional[str] = Field(None, max_length=300)
     max_teilnehmer: int           = 10
-    beschreibung:   Optional[str] = None
+    beschreibung:   Optional[str] = Field(None, max_length=5000)
 
 class WalkUpdate(BaseModel):
-    titel:          Optional[str] = None
-    datum:          Optional[str] = None
-    uhrzeit:        Optional[str] = None
+    titel:          Optional[str] = Field(None, max_length=200)
+    datum:          Optional[str] = Field(None, max_length=32)
+    uhrzeit:        Optional[str] = Field(None, max_length=20)
     lat:            Optional[float] = None
     lon:            Optional[float] = None
-    ort_name:       Optional[str] = None
+    ort_name:       Optional[str] = Field(None, max_length=300)
     max_teilnehmer: Optional[int] = None
-    beschreibung:   Optional[str] = None
+    beschreibung:   Optional[str] = Field(None, max_length=5000)
 
 class JoinRequest(BaseModel):
     dog_ids: List[int] = []   # leere Liste = ohne Hund (selten)
@@ -46,7 +46,7 @@ class InviteRequest(BaseModel):
     friend_id: int
 
 class RsvpRequest(BaseModel):
-    status: str  # 'yes' | 'maybe' | 'no'
+    status: str = Field(..., max_length=20)  # 'yes' | 'maybe' | 'no'
 
 
 # ------------------------------------------------------------------