feat: improve off-chain proposal HTML support

[EightRice]

• Updated tooltip text from "Allow markup" to "Allow HTML" for better clarity
• Increased description character limit from 1,500 to 10,000 characters
• Applies to both community creation and proposal creation forms

This improves the user experience when creating off-chain proposals with HTML-formatted descriptions.

[netlify[bot]]

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Lighthouse	1 paths audited Performance: 27 (🔴 down 2 from production) Accessibility: 91 (no change from production) Best Practices: 100 (no change from production) SEO: 92 (no change from production) PWA: 70 (no change from production) View the detailed breakdown and full score reports

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