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

internal/storage/sqlite/migrations/036_owner_column.go

@@ -0,0 +1,34 @@
+package migrations
+
+import (
+	"database/sql"
+	"fmt"
+)
+
+// MigrateOwnerColumn adds the owner column to the issues table.
+// This tracks the human owner responsible for the issue, using git author email
+// for HOP CV (curriculum vitae) attribution chains. See Decision 008.
+func MigrateOwnerColumn(db *sql.DB) error {
+	// Check if column already exists
+	var columnExists bool
+	err := db.QueryRow(`
+		SELECT COUNT(*) > 0
+		FROM pragma_table_info('issues')
+		WHERE name = 'owner'
+	`).Scan(&columnExists)
+	if err != nil {
+		return fmt.Errorf("failed to check owner column: %w", err)
+	}
+
+	if columnExists {
+		return nil
+	}
+
+	// Add the owner column
+	_, err = db.Exec(`ALTER TABLE issues ADD COLUMN owner TEXT DEFAULT ''`)
+	if err != nil {
+		return fmt.Errorf("failed to add owner column: %w", err)
+	}
+
+	return nil
+}