#8940 feat(AuditLog): Add the organisation audit log page

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Changes

Contributes to #8889

The organisation audit log page, on the endpoints from #8921. It sits behind the organisation_audit_log flag and is shown to organisation admins only.

• New Audit Log tab in the organisation nav.
• Logs grouped by day. Each row shows the project and environment, and expands to the field changes. When a log has no field changes, the row links to the related object instead.
• Search, Clear all and paging. The search lives in the URL.
• Loading, empty, no access and error states.

A new list rather than the project page's AuditLog: it uses no Flux stores, so the project page can move onto it later.

Shared changes, not behind the flag:

• Accordion gets a controlled open and a row variant, and the rows use it. Its other users (release pipeline status, environment metrics, pending change requests) keep the card look.
• ColorSwatch takes children and an xl size. The project initial in each row is built on it.
• The project palette and contrast colour move out of Utils into paletteColour, so Jest can test them. Utils still exports them, so existing callers don't change.
• New --always-black token, the pair of --always-white, for the initial on light palette colours.

Next: filtering by scope (#8941), then the stories and the RTL tests.

How did you test this code?

• Unit tests for the filters, URL round trip, day grouping, error kinds, related object links and palette colours.
• By hand against a local API: with the flag on, open Organisation → Audit Log, search, expand a row and page through.