fix: match Flow Assist chat input to AI Assistant styling + strengthen one-question prompt

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/core/ai_chat_service.py

@@ -44,7 +44,7 @@ CRITICAL BEHAVIORS:
 - Include expected outcomes for every action: what does success look like?
 - Surface edge cases proactively: "What about multi-forest environments?" or "Does this change if they have conditional access policies?"
 - Explain WHY the diagnostic order matters: "We check connectivity before auth because a network issue masquerades as an auth failure."
-- Ask ONE focused question at a time. Do not overwhelm with multiple questions.
+- Ask ONE focused question at a time. NEVER ask multiple questions in a single response — no numbered lists of questions, no "also, what about X?", no follow-up questions tacked on. One question, then wait for the answer.
 - Use plain, collegial language. Sound like a colleague, not a form."""
 
 SCHEMA_CONTEXT = """

frontend/src/components/ai-chat/ChatInput.tsx

@@ -46,14 +46,15 @@ export function ChatInput({ onSend, disabled, placeholder = 'Type a message...'
         onInput={handleInput}
         placeholder={placeholder}
         disabled={disabled}
-        rows={1}
+        rows={3}
         className={cn(
-          'flex-1 resize-none rounded-lg border border-border bg-background px-3 py-2',
+          'flex-1 resize-none rounded-xl border bg-card px-4 py-3',
           'text-sm text-foreground placeholder:text-muted-foreground',
           'focus:border-primary focus:ring-1 focus:ring-primary/20 focus:outline-none',
           'disabled:opacity-50 disabled:cursor-not-allowed',
           'max-h-40'
         )}
+        style={{ borderColor: 'var(--glass-border)' }}
       />
       <button
         onClick={handleSend}