feat: add Discover() for scanning model directories

Scans a base directory for model directories (subdirs with config.json +
*.safetensors). Returns path, architecture, quantisation info, and file
count for each discovered model. Useful for embedding in applications
that need to find available models at runtime.

Co-Authored-By: Virgil <virgil@lethean.io>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

discover.go

@@ -0,0 +1,84 @@
+package inference
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+)
+
+// DiscoveredModel describes a model directory found by Discover.
+type DiscoveredModel struct {
+	Path         string // Absolute path to the model directory
+	ModelType    string // Architecture from config.json (e.g. "gemma3", "qwen3", "llama")
+	QuantBits    int    // Quantisation bits (0 if unquantised)
+	QuantGroup   int    // Quantisation group size
+	NumFiles     int    // Number of safetensors weight files
+}
+
+// Discover scans baseDir for model directories. A valid model directory
+// contains config.json and at least one .safetensors file.
+// Scans one level deep (immediate subdirectories of baseDir).
+func Discover(baseDir string) ([]DiscoveredModel, error) {
+	entries, err := os.ReadDir(baseDir)
+	if err != nil {
+		return nil, err
+	}
+
+	var models []DiscoveredModel
+	for _, entry := range entries {
+		if !entry.IsDir() {
+			continue
+		}
+		dir := filepath.Join(baseDir, entry.Name())
+		m, ok := probeModelDir(dir)
+		if ok {
+			models = append(models, m)
+		}
+	}
+
+	// Also check baseDir itself (in case it's a model directory).
+	if m, ok := probeModelDir(baseDir); ok {
+		// Prepend so the base dir appears first.
+		models = append([]DiscoveredModel{m}, models...)
+	}
+
+	return models, nil
+}
+
+// probeModelDir checks if dir looks like a model directory.
+func probeModelDir(dir string) (DiscoveredModel, bool) {
+	configPath := filepath.Join(dir, "config.json")
+	data, err := os.ReadFile(configPath)
+	if err != nil {
+		return DiscoveredModel{}, false
+	}
+
+	// Count safetensors files.
+	matches, _ := filepath.Glob(filepath.Join(dir, "*.safetensors"))
+	if len(matches) == 0 {
+		return DiscoveredModel{}, false
+	}
+
+	absDir, _ := filepath.Abs(dir)
+
+	var probe struct {
+		ModelType    string `json:"model_type"`
+		Quantization *struct {
+			Bits      int `json:"bits"`
+			GroupSize int `json:"group_size"`
+		} `json:"quantization"`
+	}
+	_ = json.Unmarshal(data, &probe)
+
+	m := DiscoveredModel{
+		Path:      absDir,
+		ModelType: probe.ModelType,
+		NumFiles:  len(matches),
+	}
+	if probe.Quantization != nil {
+		m.QuantBits = probe.Quantization.Bits
+		m.QuantGroup = probe.Quantization.GroupSize
+	}
+
+	return m, true
+}