🎨 Palette: Improve accessibility of icon-only buttons with ARIA labels

[longestmt]

💡 What
Added missing aria-label attributes to various icon-only buttons throughout the app (modals, workout tracker, plans list) and added aria-hidden="true" to their inner <svg> icons or decorative text.

🎯 Why
Icon-only buttons rely entirely on visual cues. Without aria-label, screen reader users hear generic text like "button" with no context of what the button actually does. Adding aria-hidden="true" to the inner SVG prevents screen readers from redundantly announcing complex DOM node trees inside the button, creating a cleaner and more direct audio experience.

📸 Before/After
Before: <button class="btn btn-ghost btn-icon" title="History"><svg>...</svg></button>
After: <button class="btn btn-ghost btn-icon" title="History" aria-label="History"><svg aria-hidden="true">...</svg></button>

♿ Accessibility
Significantly improves screen reader accessibility and navigation clarity. Ensures screen readers clearly announce the purpose of critical interactive elements like "Close modal", "Swap exercise", "1RM Calculator", "Skip timer", and "Delete plan" without extra noise from inner SVGs. Fixed critical issue where aria-hidden applied to a <button> created inaccessible "ghost tab stops".

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PR created automatically by Jules for task 4254287669325776007 started by @longestmt

[google-labs-jules]

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