feat: expand components and prepare 0.2.0

[ellsphillips]

Superseded by #8.

Lineal's published entrypoint omits the theme export, and its navigation can misidentify sections or miscount progress. Version 0.2.0 restores the public API, expands the component library and gives outlines, contents and progress a tested data model.

• Add callouts, metrics, vertical/horizontal steps, repeating-header tables, comparisons and composable layouts.
• Extend code blocks with syntax styles, SVG file labels, line numbers, ranges, captions, wrapping and measured size checks.
• Build heading ownership independently of visibility. Render linked contextual outlines and flowing tables of contents with logical page numbers.
• Compute progress from authored section boundaries. Handle frozen cards, overlays, handouts, appendices and finite weight normalization; upgrade Touying to 0.7.4 while retaining Typst 0.13.1 support.
• Add documented public examples, isolated package checks and a 17-page component gallery.

Addresses #5 and #6. Universe users receive the import fix when the dependent 0.2.0 registry submission is published. The existing 0.1.0 package remains unchanged.

Validation: 120 checks each on Typst 0.13.1 and 0.14.2, with compiler warnings treated as failures. Includes 31,878 progress combinations, 124 heading sequences, overlay identity fixtures, expected-error cases and real package imports. All gallery pages were rendered and visually checked. Bundled assets include license and provenance notices.

Overlay headings support cumulative additions. Changes or removals fail explicitly; conditional display content should use ordinary styled text. The navigation guides document this boundary.

Dependent registry release draft: typst/packages#6151