🎨 Palette: Improve accessibility of icon-only buttons

[longestmt]

💡 What: Added explicit aria-label attributes to icon-only buttons across the application (like Close, Delete, Start, History, Swap, Note) and added aria-hidden="true" to their internal <svg> elements.

🎯 Why: Icon-only buttons without accessible names cannot be interpreted correctly by screen readers, creating a significant barrier for visually impaired users. Additionally, reading out the raw SVG contents is confusing. This change ensures screen readers correctly announce the button's purpose while ignoring the visual SVG markup.

📸 Before/After: Visual appearance is completely unchanged, but the accessibility tree is significantly improved.

♿ Accessibility:

• Adds aria-label attribute to icon-only buttons in src/components/modal.js, src/pages/plans.js, and src/pages/workout.js.
• Adds aria-hidden="true" to internal <svg> elements to prevent redundant or confusing screen reader announcements.

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PR created automatically by Jules for task 5219097353689213210 started by @longestmt

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