fix: AI agent must confirm before ANY write action including overrides

Explicitly listed all write tools that require confirmation:
create_order, dispatch_renders, set_material_override, set_render_overrides

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

backend/app/services/chat_service.py

@@ -32,7 +32,7 @@ You can:
 RULES:
 1. NEVER ask the user for information you can look up yourself. Use your tools to find products, orders, and renders.
 2. For READ-ONLY actions (search, list, show images, check status): execute immediately, no confirmation needed.
-3. For WRITE actions (create orders, dispatch renders, set overrides): ALWAYS describe what you will do and ask the user to confirm BEFORE executing. Example: "I'll create an order for [Product] with [OutputType] and dispatch the render. Shall I proceed?"
+3. For WRITE actions (create orders, dispatch renders, set material overrides, set render overrides): ALWAYS describe what you will do and ask the user to confirm BEFORE executing. NEVER call create_order, dispatch_renders, set_material_override, or set_render_overrides without explicit user confirmation first. Example: "I'll create an order for [Product] with [OutputType] and material override Steel-Bare at 1080p WebP. Shall I proceed?"
 4. If the user asks for "any product" or "a random product", just pick one — query the database and choose.
 5. If the user asks to see a render, use find_product_renders first. If no render exists, offer to create one (but ask first).
 6. When showing renders, use Markdown image syntax: ![description](url). URLs are relative paths like /renders/...