feat(ai): add support for Ollama AI provider configuration

* Update README with Ollama integration details
* Add Ollama configuration to example YAML files
* Implement Ollama provider in AI factory
* Add tests for Ollama provider functionality
* Enhance config validation for Ollama settings

internal/config/loader_test.go

@@ -69,3 +69,51 @@ logging:
 		t.Fatalf("server port = %d, want 9090", cfg.Server.Port)
 	}
 }
+
+func TestLoadAppliesOllamaEnvOverrides(t *testing.T) {
+	configPath := filepath.Join(t.TempDir(), "test.yaml")
+	if err := os.WriteFile(configPath, []byte(`
+server:
+  port: 8080
+mcp:
+  path: "/mcp"
+auth:
+  keys:
+    - id: "test"
+      value: "secret"
+database:
+  url: "postgres://from-file"
+ai:
+  provider: "ollama"
+  embeddings:
+    model: "nomic-embed-text"
+    dimensions: 768
+  metadata:
+    model: "llama3.2"
+  ollama:
+    base_url: "http://localhost:11434/v1"
+    api_key: "ollama"
+search:
+  default_limit: 10
+  max_limit: 50
+logging:
+  level: "info"
+`), 0o600); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
+
+	t.Setenv("OB1_OLLAMA_BASE_URL", "https://ollama.example.com/v1")
+	t.Setenv("OB1_OLLAMA_API_KEY", "remote-key")
+
+	cfg, _, err := Load(configPath)
+	if err != nil {
+		t.Fatalf("Load() error = %v", err)
+	}
+
+	if cfg.AI.Ollama.BaseURL != "https://ollama.example.com/v1" {
+		t.Fatalf("ollama base url = %q, want env override", cfg.AI.Ollama.BaseURL)
+	}
+	if cfg.AI.Ollama.APIKey != "remote-key" {
+		t.Fatalf("ollama api key = %q, want env override", cfg.AI.Ollama.APIKey)
+	}
+}