🎨 Palette: Restore placeholder on Cosmology Map interaction

[ightevenmckane187]

🎨 Palette: Restore placeholder on Cosmology Map interaction

• 💡 What: Added a visual placeholder inside #archetype-info container instructing the user to "Hover or focus an archetype node to view its mythic mandate.", and implemented mouseleave/blur event listeners on the .archetype-node elements to restore it once interaction ends.
• 🎯 Why: Previously, the #archetype-info block was completely empty and invisible until first interaction, providing no guidance to the user. Also, once a node was hovered/focused, the text remained there permanently even when the mouse left, leading to stale content.
• ♿ Accessibility: Centered placeholder styled with theme-aware text contrast (--text-color with opacity: 0.65 and italic style) ensuring the experience is clean and readable, while registering listeners for both mouse (mouseleave) and keyboard focus (blur).
• 🧪 Verification: Added a comprehensive integration test in tests/server.test.ts checking for HTML rendering of placeholder, classes, and registration of the mouseleave/blur events. Verified visually using Playwright with force=True hover triggers.

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PR created automatically by Jules for task 7597171459057242166 started by @ightevenmckane187

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