Add llm-gateway module: routing, failover below the tool-calling advisor, per-provider circuit breakers, dollar caps and token limits, tenant-keyed cache; real OpenAI and Anthropic models against a local fake

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01JXVi2GMQ7bR5EmbUFdDj7N

llm-gateway/src/main/resources/application.yml

@@ -0,0 +1,12 @@
+# Providers are plain data. Prices are dollars per million tokens (read 2026-10-09, see CostTest in the providers module).
+gateway:
+  providers:
+    - { name: openai, type: openai, base-url: "https://api.openai.com/v1", api-key: "${OPENAI_API_KEY:unset}", model: gpt-6.1-sol, input-price: "2.00", output-price: "10.00" }
+    - { name: anthropic, type: anthropic, base-url: "https://api.anthropic.com", api-key: "${ANTHROPIC_API_KEY:unset}", model: claude-sonnet-5-5, input-price: "2.00", output-price: "10.00" }
+  routes:
+    smart: [openai, anthropic]
+    fast: [anthropic, openai]
+  defaults: { budget-micros: 5000000, tokens-per-hour: 100000 }
+  tenants:
+    free-tier-tenant: { budget-micros: 50000, tokens-per-hour: 10000 }
+  breaker: { sliding-window-size: 10, minimum-calls: 5, failure-rate-threshold: 50, wait-open-millis: 30000 }