feat(phase-5): Complete dashboard UI templates

- Add posts.html: Post management with filtering by status/platform/type,
  stats display, pagination, edit modal, and actions (approve, reject,
  publish now, schedule, edit, delete)
- Add calendar.html: Visual calendar with month/week views, drag-and-drop
  rescheduling, platform filtering with color-coded status
- Add interactions.html: Interactions management with filtering, detail
  panel for responding, AI response suggestions, lead marking
- Add settings.html: API connection status, DeepSeek config, Telegram
  notifications setup, system info, and quick actions
- Update dashboard.py with settings route

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/api/routes/dashboard.py

@@ -167,3 +167,16 @@ async def dashboard_services(request: Request, db: Session = Depends(get_db)):
         "request": request,
         "user": user.to_dict()
     })
+
+
+@router.get("/settings", response_class=HTMLResponse)
+async def dashboard_settings(request: Request, db: Session = Depends(get_db)):
+    """Página de configuración."""
+    user = require_auth(request, db)
+    if not user:
+        return RedirectResponse(url="/login", status_code=302)
+
+    return templates.TemplateResponse("settings.html", {
+        "request": request,
+        "user": user.to_dict()
+    })