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/doctor/fix/deletions.go

@@ -22,11 +22,12 @@ func HydrateDeletionsManifest(path string) error {
 	}
 
 	beadsDir := filepath.Join(path, ".beads")
-	jsonlPath := filepath.Join(beadsDir, "beads.jsonl")
+	// bd-6xd: issues.jsonl is the canonical filename
+	jsonlPath := filepath.Join(beadsDir, "issues.jsonl")
 
-	// Also check for legacy issues.jsonl
+	// Also check for legacy beads.jsonl
 	if _, err := os.Stat(jsonlPath); os.IsNotExist(err) {
-		legacyPath := filepath.Join(beadsDir, "issues.jsonl")
+		legacyPath := filepath.Join(beadsDir, "beads.jsonl")
 		if _, err := os.Stat(legacyPath); err == nil {
 			jsonlPath = legacyPath
 		} else {