[mjanez]

Second pass on the asset metadata sheet (after #86), from feedback on the first.

• Header instead of a warning row: a progress ring with "N of M fields filled" and, when required fields are missing, a "Fill in required fields" button that opens the section, scrolls to the first one and starts editing it. With none missing it says so in green.
• Sections: sentence-case title, a progress bar with filled/total on the right and a "Pending: N" badge.
• Fields leave the key/value table grid for a label/value layout; the heavy tint on required rows goes, only a required field without a value is highlighted, with its edit button always visible.
• Additional metadata (the free-form entries) folds like any other section, closed by default, with its count. The KEY/VALUE header is dropped when the sheet has governed fields.
• Empty optional fields stay behind "Show fields without a value (N)".

MetadataView is shared, so products and glossary terms also get the folded additional metadata.

Prettier and check-i18n pass; ESLint only reports the two pre-existing external-link errors. Exercised in a browser against a mocked API with the dgu profile, light and dark.