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/forum.py

@@ -2,7 +2,7 @@
 
 import os, uuid, json, logging
 from fastapi import APIRouter, Depends, HTTPException, UploadFile, File
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 from typing import Optional
 from database import db
 from auth import get_current_user, get_current_user_optional
@@ -27,40 +27,40 @@ KATEGORIEN = ['allgemein', 'rasse', 'region', 'gesundheit', 'erziehung',
 # Schemas
 # ------------------------------------------------------------------
 class ThreadCreate(BaseModel):
-    kategorie:   str           = 'allgemein'
-    titel:       str
-    text:        str
+    kategorie:   str           = Field('allgemein', max_length=100)
+    titel:       str           = Field(..., min_length=3, max_length=200)
+    text:        str           = Field(..., min_length=1, max_length=10000)
     thread_lat:  Optional[float] = None
     thread_lon:  Optional[float] = None
-    thread_ort:  Optional[str]   = None
-    client_time: Optional[str]   = None
+    thread_ort:  Optional[str]   = Field(None, max_length=300)
+    client_time: Optional[str]   = Field(None, max_length=64)
 
 class PostCreate(BaseModel):
-    text:        str
-    client_time: Optional[str] = None
+    text:        str           = Field(..., min_length=1, max_length=10000)
+    client_time: Optional[str] = Field(None, max_length=64)
 
 class ThreadPatch(BaseModel):
     is_pinned:  Optional[int] = None
     is_locked:  Optional[int] = None
 
 class ThreadUpdate(BaseModel):
-    titel:      Optional[str]   = None
-    text:       Optional[str]   = None
+    titel:      Optional[str]   = Field(None, max_length=200)
+    text:       Optional[str]   = Field(None, max_length=10000)
     thread_lat: Optional[float] = None
     thread_lon: Optional[float] = None
-    thread_ort: Optional[str]   = None
+    thread_ort: Optional[str]   = Field(None, max_length=300)
 
 class PostUpdate(BaseModel):
-    text: str
+    text: str = Field(..., min_length=1, max_length=10000)
 
 class LikeBody(BaseModel):
-    target_type: str   # 'thread' | 'post'
+    target_type: str = Field(..., max_length=20)   # 'thread' | 'post'
     target_id:   int
 
 class ReportBody(BaseModel):
-    target_type: str
+    target_type: str = Field(..., max_length=20)
     target_id:   int
-    grund:       str
+    grund:       str = Field(..., min_length=3, max_length=1000)
 
 class LocationBody(BaseModel):
     lat:  Optional[float] = None