Refactor: consolidate ID generation and shared helpers (bd-0702, bd-1445)

- Created ids.go with ValidateIssueIDPrefix, GenerateIssueID, EnsureIDs
- Created issues.go with insertIssue/insertIssues helpers
- Created events_helpers.go with recordCreatedEvent/recordCreatedEvents
- Created dirty_helpers.go with markDirty/markDirtyBatch
- Refactored sqlite.go and batch_ops.go to use new helpers
- Removed duplicate code from hash_ids.go

Amp-Thread-ID: https://ampcode.com/threads/T-b1ab5a16-96de-4e4d-b255-3617055a89eb
Co-authored-by: Amp <amp@ampcode.com>

internal/storage/sqlite/dirty_helpers.go

@@ -0,0 +1,45 @@
+package sqlite
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"time"
+
+	"github.com/steveyegge/beads/internal/types"
+)
+
+// markDirty marks a single issue as dirty for incremental export
+func markDirty(ctx context.Context, conn *sql.Conn, issueID string) error {
+	_, err := conn.ExecContext(ctx, `
+		INSERT INTO dirty_issues (issue_id, marked_at)
+		VALUES (?, ?)
+		ON CONFLICT (issue_id) DO UPDATE SET marked_at = excluded.marked_at
+	`, issueID, time.Now())
+	if err != nil {
+		return fmt.Errorf("failed to mark issue dirty: %w", err)
+	}
+	return nil
+}
+
+// markDirtyBatch marks multiple issues as dirty for incremental export
+func markDirtyBatch(ctx context.Context, conn *sql.Conn, issues []*types.Issue) error {
+	stmt, err := conn.PrepareContext(ctx, `
+		INSERT INTO dirty_issues (issue_id, marked_at)
+		VALUES (?, ?)
+		ON CONFLICT (issue_id) DO UPDATE SET marked_at = excluded.marked_at
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to prepare dirty statement: %w", err)
+	}
+	defer func() { _ = stmt.Close() }()
+
+	dirtyTime := time.Now()
+	for _, issue := range issues {
+		_, err = stmt.ExecContext(ctx, issue.ID, dirtyTime)
+		if err != nil {
+			return fmt.Errorf("failed to mark issue %s dirty: %w", issue.ID, err)
+		}
+	}
+	return nil
+}