fix: ensure production uses DB-configured model/provider from UI

- Migration 026: update seed defaults from ollama to vllm/AxionML
- Migration 031: fix existing rows still on old ollama defaults
- Helm values: set OLLAMA_BASE_URL to cluster ollama endpoint (was empty)
- Extractor: guard against switching to ollama when base_url is empty
- OllamaClient: validate base_url on construction to fail fast

infra/migrations/031_fix_agent_defaults.sql

@@ -0,0 +1,13 @@
+-- Fix agent default model_provider and model_name to match production config.
+-- The original migration 026 seeded with 'ollama'/'qwen3.5:9b-fast' but production
+-- uses vLLM. This migration updates agents that still have the old defaults,
+-- preserving any user customizations (only updates if model_name matches the old default).
+
+UPDATE ai_agents
+   SET model_provider = 'vllm',
+       model_name = 'AxionML/Qwen3.5-9B-NVFP4',
+       max_tokens = 4096,
+       updated_at = NOW()
+ WHERE slug IN ('document-extractor', 'event-classifier', 'thesis-rewriter')
+   AND source = 'system'
+   AND model_name = 'qwen3.5:9b-fast';