feat: add owner field for human attribution in HOP CV chains

Add 'owner' field to Issue struct for tracking the human responsible
for the issue, distinct from 'created_by' which tracks the executor.
Owner is populated from git author email (GIT_AUTHOR_EMAIL or git
config user.email), per Decision 008 for CV accumulation.

Changes:
- Add Owner field to types.Issue with omitempty JSON tag
- Include Owner in content hash computation
- Add owner column migration (036_owner_column.go)
- Update all SQL queries to include owner field
- Add getOwner() helper using git author email fallback chain
- Populate owner in bd create command
- Add owner to RPC CreateArgs protocol

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

Executed-By: beads/crew/dave
Rig: beads
Role: crew

cmd/bd/main.go

@@ -143,6 +143,27 @@ func getActorWithGit() string {
 	return "unknown"
 }
 
+// getOwner returns the human owner for CV attribution.
+// Priority: GIT_AUTHOR_EMAIL env > git config user.email > "" (empty)
+// This is the foundation for HOP CV (curriculum vitae) chains per Decision 008.
+// Unlike actor (which tracks who executed), owner tracks the human responsible.
+func getOwner() string {
+	// Check GIT_AUTHOR_EMAIL first - this is set during git commit operations
+	if authorEmail := os.Getenv("GIT_AUTHOR_EMAIL"); authorEmail != "" {
+		return authorEmail
+	}
+
+	// Fall back to git config user.email - the natural default
+	if out, err := exec.Command("git", "config", "user.email").Output(); err == nil {
+		if gitEmail := strings.TrimSpace(string(out)); gitEmail != "" {
+			return gitEmail
+		}
+	}
+
+	// Return empty if no email found (owner is optional)
+	return ""
+}
+
 func init() {
 	// Initialize viper configuration
 	if err := config.Initialize(); err != nil {