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/routers/content.py

@@ -96,12 +96,12 @@ def generate_content(
     text = generate_post_text(
         character=char_dict,
         llm_provider=llm,
-        platform=request.platform,
+        platform=request.effective_platform,
         topic_hint=request.topic_hint,
     )
 
     # Generate hashtags
-    hashtags = generate_hashtags(text, llm, request.platform)
+    hashtags = generate_hashtags(text, llm, request.effective_platform)
 
     # Handle affiliate links
     affiliate_links_used: list[dict] = []