feat(types): add template molecules infrastructure for beads-1ra

Add support for template molecules (is_template field and TypeMolecule type):

- Add IsTemplate field to Issue type with JSON support
- Add TypeMolecule constant to IssueType constants
- Add IsTemplate filter to IssueFilter for querying
- Update all SQL queries to include is_template column
- Add migration 024 for is_template column
- Add FindMoleculesJSONLInDir helper for molecules.jsonl path detection

This enables treating certain issues as read-only templates that can be
instantiated to create work items. The template flag allows separating
template molecules from regular work items in queries and exports.

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

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

internal/storage/sqlite/multirepo.go

@@ -265,6 +265,10 @@ func (s *SQLiteStorage) upsertIssueInTx(ctx context.Context, tx *sql.Tx, issue *
 	if issue.Pinned {
 		pinned = 1
 	}
+	isTemplate := 0
+	if issue.IsTemplate {
+		isTemplate = 1
+	}
 
 	if err == sql.ErrNoRows {
 		// Issue doesn't exist - insert it
@@ -274,8 +278,8 @@ func (s *SQLiteStorage) upsertIssueInTx(ctx context.Context, tx *sql.Tx, issue *
 				status, priority, issue_type, assignee, estimated_minutes,
 				created_at, updated_at, closed_at, external_ref, source_repo, close_reason,
 				deleted_at, deleted_by, delete_reason, original_type,
-				sender, ephemeral, pinned
-			) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+				sender, ephemeral, pinned, is_template
+			) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
 		`,
 			issue.ID, issue.ContentHash, issue.Title, issue.Description, issue.Design,
 			issue.AcceptanceCriteria, issue.Notes, issue.Status,
@@ -283,7 +287,7 @@ func (s *SQLiteStorage) upsertIssueInTx(ctx context.Context, tx *sql.Tx, issue *
 			issue.EstimatedMinutes, issue.CreatedAt, issue.UpdatedAt,
 			issue.ClosedAt, issue.ExternalRef, issue.SourceRepo, issue.CloseReason,
 			issue.DeletedAt, issue.DeletedBy, issue.DeleteReason, issue.OriginalType,
-			issue.Sender, ephemeral, pinned,
+			issue.Sender, ephemeral, pinned, isTemplate,
 		)
 		if err != nil {
 			return fmt.Errorf("failed to insert issue: %w", err)
@@ -307,7 +311,7 @@ func (s *SQLiteStorage) upsertIssueInTx(ctx context.Context, tx *sql.Tx, issue *
 					issue_type = ?, assignee = ?, estimated_minutes = ?,
 					updated_at = ?, closed_at = ?, external_ref = ?, source_repo = ?,
 					deleted_at = ?, deleted_by = ?, delete_reason = ?, original_type = ?,
-					sender = ?, ephemeral = ?, pinned = ?
+					sender = ?, ephemeral = ?, pinned = ?, is_template = ?
 				WHERE id = ?
 			`,
 				issue.ContentHash, issue.Title, issue.Description, issue.Design,
@@ -315,7 +319,7 @@ func (s *SQLiteStorage) upsertIssueInTx(ctx context.Context, tx *sql.Tx, issue *
 				issue.IssueType, issue.Assignee, issue.EstimatedMinutes,
 				issue.UpdatedAt, issue.ClosedAt, issue.ExternalRef, issue.SourceRepo,
 				issue.DeletedAt, issue.DeletedBy, issue.DeleteReason, issue.OriginalType,
-				issue.Sender, ephemeral, pinned,
+				issue.Sender, ephemeral, pinned, isTemplate,
 				issue.ID,
 			)
 			if err != nil {