Polish Memory selects and add a Midnight dark preset for eye comfort

[quangdo126]

Summary

• Replaced native <select> controls in Memory page and Memory create dialog with the shared Select component for consistent spacing and styling.
• Added a color preset selector in the top header.
• Added a new Midnight preset that only adjusts dark-mode background/surface tokens to neutral black tones.
• Kept light mode unchanged and preserved important semantic colors.

Why

In prolonged night-time use, the current dark palette can feel visually fatiguing because:

• Dark surfaces still carry warm/brown chroma, which appears brighter than neutral blacks.
• Bright layers on top of warm dark surfaces can increase perceived glare and make contrast feel harsh.
• During long sessions (especially scanning dense forms/tables), this can increase visual adaptation load and lead to eye strain.

This change introduces a Midnight preset that only neutralizes dark-mode background/surface tones for better night comfort.

To respect the original design direction, light theme remains unchanged, and key semantic/brand colors in dark mode are intentionally preserved.

Validation

• pnpm -C ui/web build

[mrgoonie]

@claude review

[claude]

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[quangdo126]

Updated after rebase/conflict resolution:

• Resolved conflicts in topbar and locale files (vi/zh).
• Added the same Select polish to Knowledge Graph page to keep select behavior/style consistent with Memory page.
• No backend logic changes.