feat: sync all BRAIN mobile changes - onboarding, cookies, legal, mobile UX, settings

- Add OnboardingWizard, BetaBanner, CookieBanner components
- Add legal pages (Privacy, Terms, Cookies)
- Update Layout with mobile topbar, sidebar drawer, plan banner
- Update SettingsPage with profile, API config, security
- Update CharacterForm with topic suggestions, niche chips
- Update EditorialCalendar with shared strategy card
- Update ContentPage with narrative technique + brief
- Update SocialAccounts with 4 platforms and token guides
- Fix CSS button color inheritance, mobile responsive
- Add backup script
- Update .gitignore for pgdata and backups

Co-Authored-By: Claude (BRAIN/StackOS) <noreply@anthropic.com>

backend/app/schemas.py

@@ -1,5 +1,5 @@
 from datetime import datetime
-from typing import Optional
+from typing import List, Optional
 
 from pydantic import BaseModel
 
@@ -103,13 +103,23 @@ class PostResponse(BaseModel):
 
 class GenerateContentRequest(BaseModel):
     character_id: int
-    platform: str = "instagram"
-    content_type: str = "text"
+    platform: str = "instagram"           # legacy single-platform (kept for compat)
+    content_type: str = "text"             # legacy single type (kept for compat)
+    platforms: List[str] = []              # new: multi-platform (overrides platform if non-empty)
+    content_types: List[str] = []          # new: multi-type (overrides content_type if non-empty)
     topic_hint: Optional[str] = None
     include_affiliates: bool = True
-    provider: Optional[str] = None  # override default LLM
+    provider: Optional[str] = None
     model: Optional[str] = None
 
+    @property
+    def effective_platform(self) -> str:
+        return self.platforms[0] if self.platforms else self.platform
+
+    @property
+    def effective_content_type(self) -> str:
+        return self.content_types[0] if self.content_types else self.content_type
+
 
 class GenerateImageRequest(BaseModel):
     character_id: int