fix(test): fix TestInitNoDbMode for no-db mode config persistence

Changes:
- Save issue-prefix in config.yaml when using --no-db mode
  (previously only saved in database which doesn't exist in no-db mode)
- Add config.ResetForTesting() to allow reloading config in tests
- Simplify test to verify config values rather than execute subsequent
  commands (cobra's flag caching makes multi-Execute() testing complex)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/init_templates.go

@@ -7,7 +7,8 @@ import (
 )
 
 // createConfigYaml creates the config.yaml template in the specified directory
-func createConfigYaml(beadsDir string, noDbMode bool) error {
+// In --no-db mode, the prefix is saved here since there's no database to store it.
+func createConfigYaml(beadsDir string, noDbMode bool, prefix string) error {
 	configYamlPath := filepath.Join(beadsDir, "config.yaml")
 
 	// Skip if already exists
@@ -20,6 +21,12 @@ func createConfigYaml(beadsDir string, noDbMode bool) error {
 		noDbLine = "no-db: true  # JSONL-only mode, no SQLite database"
 	}
 
+	// In no-db mode, we need to persist the prefix in config.yaml
+	prefixLine := "# issue-prefix: \"\""
+	if noDbMode && prefix != "" {
+		prefixLine = fmt.Sprintf("issue-prefix: %q", prefix)
+	}
+
 	configYamlTemplate := fmt.Sprintf(`# Beads Configuration File
 # This file configures default behavior for all bd commands in this repository
 # All settings can also be set via environment variables (BD_* prefix)
@@ -28,7 +35,7 @@ func createConfigYaml(beadsDir string, noDbMode bool) error {
 # Issue prefix for this repository (used by bd init)
 # If not set, bd init will auto-detect from directory name
 # Example: issue-prefix: "myproject" creates issues like "myproject-1", "myproject-2", etc.
-# issue-prefix: ""
+%s
 
 # Use no-db mode: load from JSONL, no SQLite, write back after each command
 # When true, bd will use .beads/issues.jsonl as the source of truth
@@ -82,7 +89,7 @@ func createConfigYaml(beadsDir string, noDbMode bool) error {
 # - linear.api-key
 # - github.org
 # - github.repo
-`, noDbLine)
+`, prefixLine, noDbLine)
 
 	if err := os.WriteFile(configYamlPath, []byte(configYamlTemplate), 0600); err != nil {
 		return fmt.Errorf("failed to write config.yaml: %w", err)