Text export views: CSV, JSON, Markdown via Rhai scripts

[careck]

Summary

Add script-driven export of notes to CSV, JSON, and Markdown. Export views are registered per-schema in Rhai scripts using three new functions — register_csv_export, register_json_export, register_markdown_export — following the same deferred binding pattern as register_view.

Exports are anchored on container/folder notes. The script callback drives traversal (iterating children, following links, filtering by tag) using the full QueryContext already available to view closures.

Key Design Decisions

• Three format-specific registration functions — each with a tailored return type (CSV: Array<Map> with flat scalar values, JSON: Array<Map> with arbitrary nesting, Markdown: String)
• Preview before save — clicking an export opens a preview dialog; from there the user can save to file or copy to clipboard
• Context menu trigger — right-click a note → "Export" submenu lists available exports for that schema
• note.to_map() helper — convenience function that flattens a note into a single-level map for easy CSV/JSON authoring
• Expand build_note_map() — expose all Note properties to Rhai (currently missing: parent_id, position, created_at, modified_at, created_by, modified_by, is_expanded, schema_version). Benefits existing register_view closures too.

Script API Example

register_csv_export("BookCollection", "Book List", |note| {
    let books = get_children(note.id);
    let rows = [];
    for book in books {
        rows.push(#{
            title: book.title,
            author: book.fields["author"] ?? "",
            rating: book.fields["rating"] ?? ""
        });
    }
    rows
});

Scope

Rust Core (krillnotes-core)

• Three new BindingKind variants + registration functions in engine.rs
• ExportFormat enum + ExportRegistration struct in schema.rs
• export_registrations HashMap in SchemaRegistry
• Workspace::run_export() and Workspace::list_exports() methods
• to_map() Rhai helper function
• Expand build_note_map() with all Note fields

Tauri Commands

• list_note_exports — returns available exports for a note
• run_note_export — executes export callback, returns content string

Frontend

• Context menu "Export" submenu in ContextMenu.tsx
• New ExportPreviewDialog.tsx — preview content, save to file, copy to clipboard
• i18n keys across all 7 locales

Example Scripts

• Add CSV, JSON, Markdown exports to book-collection.rhai

Design Spec

Full spec: docs/superpowers/specs/2026-04-29-text-export-views-design.md