4. Update Storybook Stories

[MitchellShiell]

Add Storybook stories for the custom columns feature. The PCGL fixture already contains rich field-level meta data including mappings (a nested object with FHIR, mCODE, Phenopacket, and other keys) and examples (an array). Use these as the data source.

Stories to cover:

• Single column: one custom column configured, showing a simple string value from field meta
• Multiple columns: two or more columns configured, including an array value and a nested object property
• Rich component: a columnComponent that combines multiple field properties or uses custom styling, demonstrating capability beyond plain text display
• URL rendering: a column using MetaValueRenderer against a URL-valued meta property from the enriched fixture, showing a clickable hyperlink in the cell
• Column visibility: the "Columns" control in the toolbar with one custom column hidden by default via defaultVisible: false
• Sparse coverage: a column configured for a meta property that not all fields have, showing empty cells alongside populated cells
• No custom columns: confirms no regressions to the existing four-column table when customColumns is omitted

Acceptance Criteria

• All stories render without errors using the PCGL fixture
• Each story is labelled clearly in the Storybook sidebar
• Stories are grouped under an appropriate section in the viewer-table category
• The URL rendering story uses fixture data from Ticket 6 and produces a visible anchor element in at least one cell
• The rich component story demonstrates something that could not be achieved with a simple text read of a single meta property

Dependencies

Tickets 3, 4, 5, 6