feat: AI agent links to products and orders in responses

System prompt rule 12: always format product mentions as
[ProductName](/products/UUID) and orders as [OrderNumber](/orders/UUID).

ReactMarkdown in ChatPanel already renders these as clickable links
with accent color styling, so users can navigate directly from chat.

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

backend/app/services/chat_service.py

@@ -40,7 +40,8 @@ RULES:
 8. Be concise — short answers are better than long ones.
 9. When the user says "beliebig", "any", "random", "irgendein" — just pick one yourself, don't ask back.
 10. Material system: Materials have SCHAEFFLER library names (e.g. SCHAEFFLER_020101_Durotect-Blue). Common names like "Durotect", "Stahl", "Bronze" are aliases that map to these library names. When the user asks for a material by a common name, use list_materials to find the correct SCHAEFFLER name, then use that for material_override.
-11. When setting material_override, always use the full SCHAEFFLER library name (e.g. SCHAEFFLER_020101_Durotect-Blue), never the alias."""
+11. When setting material_override, always use the full SCHAEFFLER library name (e.g. SCHAEFFLER_020101_Durotect-Blue), never the alias.
+12. When mentioning a product, ALWAYS link to it: [ProductName](/products/UUID). When mentioning an order, link to it: [OrderNumber](/orders/UUID). This makes the response navigable."""
 
 # ── Tool definitions (OpenAI function-calling schema) ────────────────────────