🎨 Palette: Add native tooltips and keyboard shortcuts to Window controls

[schmug]

💡 What: Added native browser tooltips (title attributes) to the macOS-style traffic light window controls (close, minimize, maximize) and explicitly surfaced the (⌘W) keyboard shortcut for the close button.
🎯 Why: MacOS-style color-only window controls can be unintuitive for non-macOS users. Adding hover tooltips makes their functionality discoverable. Surfacing the keyboard shortcut educates power users.
♿ Accessibility: Updated aria-labels and screen-reader-only text to include the keyboard shortcut, improving navigation context for assistive technologies. Also added a critical learning to .Jules/palette.md.

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PR created automatically by Jules for task 5403379861961802859 started by @schmug

[google-labs-jules]

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[schmug]

@google-labs-jules Please rebase against main and drop .Jules/palette.md from this PR. The Jules agent log files are now gitignored as of #60 — they should not be committed. The Verify check is failing only on prettier formatting of that log file, not on the actual code change. Once rebased, this should be ready to merge.

[google-labs-jules]

@google-labs-jules Please rebase against main and drop .Jules/palette.md from this PR. The Jules agent log files are now gitignored as of #60 — they should not be committed. The Verify check is failing only on prettier formatting of that log file, not on the actual code change. Once rebased, this should be ready to merge.

I have successfully dropped the .Jules/palette.md file from this PR and rebased against the latest main branch. The actual UX enhancements remain intact.