Accessibility fixes on recent features added

[TheDancingClown]

📝 A short description of the changes

• Where the visuallyhidden class was used for the text 'No documents attached', this was read by screen readers even when documents had been attached. These have been replaced with hide class which has display: none style.
• Improved messages to be more specific to the sidebar section
• Added a column header to the Overall Turnover Growth table. Also changed table headers to match the table headings.
• Changed word count text to a darker grey to fix contrast issue against grey background

🔗 Link to the relevant story (or stories)

• https://app.asana.com/0/1200504523179345/1207135606763709

Deployment implications

• None

✅ Checklist

• Features that cannot go live are behind a feature flag/env var or specify deploy date and open PR as draft
• I have checked that commit messages make sense and explain the reasoning for each change
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have squashed any unnecessary or part-finished commits

🖼️ Screenshots (if appropriate - no PII/Prod data):