add routing service (#814)

fixes https://github.com/katanemo/plano/issues/810

demos/llm_routing/model_routing_service/demo.sh

@@ -0,0 +1,65 @@
+#!/bin/bash
+set -e
+
+PLANO_URL="${PLANO_URL:-http://localhost:12000}"
+
+echo "=== Model Routing Service Demo ==="
+echo ""
+echo "This demo shows how to use the /routing/v1/* endpoints to get"
+echo "routing decisions without actually proxying the request to an LLM."
+echo ""
+
+# --- Example 1: OpenAI Chat Completions format ---
+echo "--- 1. Code generation query (OpenAI format) ---"
+echo ""
+curl -s "$PLANO_URL/routing/v1/chat/completions" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "model": "gpt-4o-mini",
+    "messages": [
+      {"role": "user", "content": "Write a Python function that implements binary search on a sorted array"}
+    ]
+  }' | python3 -m json.tool
+echo ""
+
+# --- Example 2: Complex reasoning query ---
+echo "--- 2. Complex reasoning query (OpenAI format) ---"
+echo ""
+curl -s "$PLANO_URL/routing/v1/chat/completions" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "model": "gpt-4o-mini",
+    "messages": [
+      {"role": "user", "content": "Explain the trade-offs between microservices and monolithic architectures, considering scalability, team structure, and operational complexity"}
+    ]
+  }' | python3 -m json.tool
+echo ""
+
+# --- Example 3: Simple query (no routing match) ---
+echo "--- 3. Simple query - no routing match (OpenAI format) ---"
+echo ""
+curl -s "$PLANO_URL/routing/v1/chat/completions" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "model": "gpt-4o-mini",
+    "messages": [
+      {"role": "user", "content": "What is the capital of France?"}
+    ]
+  }' | python3 -m json.tool
+echo ""
+
+# --- Example 4: Anthropic Messages format ---
+echo "--- 4. Code generation query (Anthropic format) ---"
+echo ""
+curl -s "$PLANO_URL/routing/v1/messages" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "model": "gpt-4o-mini",
+    "max_tokens": 1024,
+    "messages": [
+      {"role": "user", "content": "Create a REST API endpoint in Rust using actix-web that handles user registration"}
+    ]
+  }' | python3 -m json.tool
+echo ""
+
+echo "=== Demo Complete ==="