docs: update README and add accessibility and sustainability document…

[oscarog]

Purpose

Update our documentation to reflect the current implementation and explain our accessibility and sustainability choices.

Changes

• Correct navigation, data fetching, setup, and feature descriptions.
• Update test filenames, coverage, and results.
• Add contributions for all four members.
• Add a linked accessibility and sustainability document with implementation examples, verification results, limitations, and improvements.
• Keep our existing structure and collective “we” tone.

Related issues

Closes #93
Closes #76

Verification

Not applicable

Screenshots

Not applicable, documentation-only changes.

Checklist

• I have reviewed my own changes.
• The changes meet the linked issue's acceptance criteria, where applicable.
• I have verified the changes and recorded the results above.
• I have added or updated tests where needed — no test changes required.
• I have updated documentation where needed.
• I have included screenshots for visual changes, or marked them not applicable.

[ludvigz]

LGTM