kbsearch: Go implementation with daemon model serving

- New nested module bin/kbsearch with Go implementation of bin/kb/search
- Embedding model (potion-multilingual-128M) served by localhost daemon
  so repeated CLI calls reuse the loaded model
- Bash launcher bin/kb/search builds binary on first run, caches to var/bin/
- Hybrid FTS + vector search (RRF k=60) matching Python kblib behavior
- YAML output via port of yamlout.py (ordered keys, same format)
- JSON output with proper field order
- All flags: --root, --repo, -n, --json, --list-model
- Root go.mod reverted to 1.25.0 (kbsearch is isolated nested module)
- CI passes: go test ./... and go vet ./... unaffected by kbsearch

bin/kbsearch/brain.go

@@ -0,0 +1,88 @@
+// Brain connection management using go-ladybug.
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	lbug "github.com/LadybugDB/go-ladybug"
+)
+
+var (
+	db   *lbug.Database
+	conn *lbug.Connection
+)
+
+func repoRoot() string {
+	// Try KB_ROOT env, then walk up from binary
+	if v := os.Getenv("KB_ROOT"); v != "" {
+		return v
+	}
+	self, err := os.Executable()
+	if err == nil {
+		dir := filepath.Dir(self)
+		for i := 0; i < 5; i++ {
+			if _, err := os.Stat(filepath.Join(dir, "var")); err == nil {
+				return dir
+			}
+			if _, err := os.Stat(filepath.Join(dir, ".git")); err == nil {
+				return dir
+			}
+			parent := filepath.Dir(dir)
+			if parent == dir {
+				break
+			}
+			dir = parent
+		}
+	}
+	return "."
+}
+
+func dbPath() string {
+	return filepath.Join(repoRoot(), "var", "kb.lbug")
+}
+
+func openBrain() error {
+	return openWithOpts(2, eps())
+}
+
+func openWithOpts(allow int, epsv string) error {
+	cfg := lbug.DefaultSystemConfig()
+	cfg.MaxNumThreads = 8
+	cfg.BufferPoolSize = 1 << 30 // 1GB
+
+	var err error
+	db, err = lbug.OpenDatabase(dbPath(), cfg)
+	if err != nil {
+		return fmt.Errorf("OpenDatabase: %w", err)
+	}
+	if epsv != "" {
+		if _, err := conn.Query("SET STREAM_SANDBOX = '" + epsv + "'"); err != nil {
+			return err
+		}
+	}
+
+	conn, err = lbug.OpenConnection(db)
+	if err != nil {
+		return fmt.Errorf("OpenConnection: %w", err)
+	}
+	if _, err := conn.Query("LOAD EXTENSION FTS"); err != nil {
+		return fmt.Errorf("LOAD EXTENSION FTS: %w", err)
+	}
+	if _, err := conn.Query("LOAD EXTENSION VECTOR"); err != nil {
+		return fmt.Errorf("LOAD EXTENSION VECTOR: %w", err)
+	}
+	return nil
+}
+
+func closeBrain() {
+	if conn != nil {
+		conn.Close()
+		conn = nil
+	}
+	if db != nil {
+		db.Close()
+		db = nil
+	}
+}