feat: mobile UX fixes + Phase C one-click generation

Mobile UX:
- index.css: comprehensive mobile media queries — headings scale down,
  touch targets enforced, grid-2col-mobile collapse class, tablet breakpoint
- ContentArchive/ContentPage: grid minmax uses min(100%, Npx) to prevent
  overflow on small screens
- CharacterForm: visual style + rules editor grids collapse on mobile
- Dashboard: stat cards grid mobile-safe
- Layout: better nav touch targets, footer responsive gap

Phase C — One-Click Generation:
- Backend: GET /api/content/suggestions endpoint — LLM generates 3 topic
  ideas based on character profile and avoids repeating recent posts
- Dashboard: "Suggerimenti per oggi" section loads suggestions on mount,
  each card links to /content with prefilled topic + character
- ContentPage: reads ?topic= and ?character= URL params, auto-fills form
  and auto-triggers generation (one-click flow from Dashboard)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/routers/content.py

@@ -340,3 +340,78 @@ def approve_post(
     db.commit()
     db.refresh(post)
     return post
+
+
+@router.get("/suggestions")
+def get_topic_suggestions(
+    character_id: int | None = Query(None),
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Suggest 3 content topics based on character profile and recent posts."""
+    if character_id:
+        character = (
+            db.query(Character)
+            .filter(Character.id == character_id, Character.user_id == current_user.id)
+            .first()
+        )
+    else:
+        character = (
+            db.query(Character)
+            .filter(Character.user_id == current_user.id, Character.is_active == True)
+            .first()
+        )
+    if not character:
+        return {"suggestions": [], "character_id": None}
+
+    provider_name = _get_setting(db, "llm_provider", current_user.id)
+    api_key = _get_setting(db, "llm_api_key", current_user.id)
+    model = _get_setting(db, "llm_model", current_user.id)
+
+    if not provider_name or not api_key:
+        return {"suggestions": [], "character_id": character.id, "needs_setup": True}
+
+    recent_posts = (
+        db.query(Post)
+        .filter(Post.character_id == character.id)
+        .order_by(Post.created_at.desc())
+        .limit(5)
+        .all()
+    )
+    recent_topics = [p.text_content[:100] for p in recent_posts if p.text_content]
+    recent_str = "\n".join(f"- {t}" for t in recent_topics) if recent_topics else "Nessun post recente."
+
+    base_url = _get_setting(db, "llm_base_url", current_user.id)
+    llm = get_llm_provider(provider_name, api_key, model, base_url=base_url)
+
+    topics = character.topics or []
+    niche = character.niche or "general"
+    target = character.target_audience or ""
+
+    system_prompt = (
+        "Sei un social media strategist esperto. "
+        "Suggerisci 3 idee per post social, ciascuna su una riga. "
+        "Ogni idea deve essere una frase breve (max 15 parole) che descrive il topic. "
+        "Non numerare, non aggiungere spiegazioni. Solo 3 righe, una per idea."
+    )
+
+    prompt = (
+        f"Personaggio: {character.name}, nicchia: {niche}\n"
+        f"Topic abituali: {', '.join(topics) if topics else 'generici'}\n"
+        f"Target: {target}\n"
+        f"Post recenti (evita ripetizioni):\n{recent_str}\n\n"
+        f"Suggerisci 3 idee per post nuovi e diversi dai recenti:"
+    )
+
+    try:
+        result = llm.generate(prompt, system=system_prompt)
+        lines = [line.strip() for line in result.strip().splitlines() if line.strip()]
+        suggestions = lines[:3]
+    except Exception:
+        suggestions = []
+
+    return {
+        "suggestions": suggestions,
+        "character_id": character.id,
+        "character_name": character.name,
+    }