Expand the size of the Footer Memo or alternate field and allow basic html/markdown

🔍 Problem Statement
As an admin, I experience the invoice footer memo being limited to 250 characters with no formatting support, which prevents including required Terms of Service language in customer invoices.

💡 User Story
As an admin, I want to write a longer footer memo (500+ characters) with basic markdown formatting, so that I can include complete Terms of Service references on invoices without truncation.

🎯 Definition of Done
- Given the invoice footer memo field, when saving content exceeding 250 characters with basic markdown, then the full content is saved and rendered on invoices.
- This change impacts the UI (invoice settings) and API (invoice template endpoint).
- Limitations: max character limit TBD by engineering; only basic formatting (bold, italic, line breaks) is supported — not full HTML.

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The footer memo is currently limited to 250 characters. We would like to reiterate some of our Terms of Service and the ideal place to include this is either in Invoice footer memo Another option might be to allow for an additional memo field that would appear below the invoice footer memo and above the Privacy Policy and Terms of Service links. The current memo fields also do not allow for any kind of basic html to be included (perhaps through Markdown). Specifically, bold, italics, bullets, numbered lists, line breaks etc. Currently it is just one long line of text. See example of how it appears currently. Certain information is blurred on purpose.