bd-6xd: Standardize on issues.jsonl as canonical filename

- Change default JSONL filename from beads.jsonl to issues.jsonl
- Add bd doctor check and fix to auto-migrate legacy beads.jsonl configs
- Update FindJSONLPath to prefer issues.jsonl over beads.jsonl
- Add CheckLegacyJSONLConfig and CheckLegacyJSONLFilename checks
- Add LegacyJSONLConfig fix to rename files and update config
- Update .gitattributes to reference issues.jsonl
- Fix tests to expect new canonical filename
- Add bd-6xd to v0.25.1 release notes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

cmd/bd/init_contributor.go

@@ -120,8 +120,8 @@ func runContributorWizard(ctx context.Context, store storage.Storage) error {
 			return fmt.Errorf("failed to create .beads in planning repo: %w", err)
 		}
 
-		// Create issues.jsonl
-		jsonlPath := filepath.Join(beadsDir, "beads.jsonl")
+		// Create issues.jsonl (canonical name, bd-6xd)
+		jsonlPath := filepath.Join(beadsDir, "issues.jsonl")
 		// #nosec G306 -- planning repo JSONL must be shareable across collaborators
 		if err := os.WriteFile(jsonlPath, []byte{}, 0644); err != nil {
 			return fmt.Errorf("failed to create issues.jsonl: %w", err)
@@ -183,8 +183,8 @@ Created by: bd init --contributor
 	fmt.Printf("\n%s %s\n\n", green("✓"), bold("Contributor setup complete!"))
 
 	fmt.Println("Configuration:")
-	fmt.Printf("  Current repo issues: %s\n", cyan(".beads/beads.jsonl"))
-	fmt.Printf("  Planning repo issues: %s\n", cyan(filepath.Join(planningPath, ".beads/beads.jsonl")))
+	fmt.Printf("  Current repo issues: %s\n", cyan(".beads/issues.jsonl"))
+	fmt.Printf("  Planning repo issues: %s\n", cyan(filepath.Join(planningPath, ".beads/issues.jsonl")))
 	fmt.Println()
 	fmt.Println("How it works:")
 	fmt.Println("  • Issues you create will route to the planning repo")