Add configurable LLM gateway with ordered failover and durable retries

config/llm.example.toml

@@ -0,0 +1,39 @@
+# Copy to an untracked config/llm.local.toml. Array order is failover order.
+[llm]
+max_attempts = 10                  # Full rounds, not individual HTTP calls
+retry_delay_seconds = 60
+blocked_retry_seconds = 3600       # Earliest explicit restart after exhaustion
+max_request_bytes = 1048576
+max_response_bytes = 1048576
+privacy_profile = "local_only"     # local_only / self_hosted / cloud_allowed
+
+[[llm.providers]]
+id = "local"
+adapter = "openai_compatible"
+privacy = "local"
+base_url = "http://127.0.0.1:8000/v1"
+model = "your-local-model"
+timeout_seconds = 30
+response_format = "json_object"
+token_parameter = "max_tokens"
+max_output_tokens = 4096
+
+[[llm.providers]]
+id = "own-server"
+adapter = "openai_compatible"
+privacy = "self_hosted"
+base_url = "https://your-server.example/v1"
+model = "your-server-model"
+api_key_env = "VBA_OWN_SERVER_KEY"
+enabled = false
+response_format = "json_object"
+
+[[llm.providers]]
+id = "cloud"
+adapter = "openai_compatible"
+privacy = "cloud"
+base_url = "https://api.openai.com/v1"
+model = "your-cloud-model"
+api_key_env = "OPENAI_API_KEY"
+enabled = false
+response_format = "json_schema"