fix(theme): differentiate button variants and project card accents

[Copilot]

Secondary and outline buttons were visually identical in dark mode. Primary and neutral project cards lacked sufficient contrast in both light and dark modes.

Button variants

Secondary: Added filled background (15-25% blue), stronger borders (50-75% opacity), box shadows
Outline: Remains transparent with subtle borders (35-40% opacity)

/* Before: identical in dark mode */
[data-theme="dark"] .secondary,
[data-theme="dark"] .outline {
  color: #ffffff;
  border-color: rgba(255, 255, 255, 0.4);
}

/* After: distinct visual hierarchy */
[data-theme="dark"] .secondary {
  background: rgba(25, 152, 255, 0.25);
  border-color: rgba(25, 152, 255, 0.6);
  box-shadow: 0 2px 8px rgba(25, 152, 255, 0.2);
}

[data-theme="dark"] .outline {
  color: #ffffff;
  border-color: rgba(255, 255, 255, 0.4);
}

Project card accents

Primary: Gradient backgrounds (blue→orange), brand-colored borders, enhanced shadows
Neutral: Pure white in light mode, subtle gray (5% opacity) in dark mode, neutral borders

Before

After

Original prompt

---

This section details on the original issue you should resolve

<issue_title>feat: UI enhancements</issue_title>
<issue_description>### HoverkraftButton

Secondary and outline HoverkraftButton have the same style.

Make them different.

Constraints

Ensure rendering respect accessibility constraints, and have an awesome look and feel in these cobined context

• light /dark mode
• inside / outside HoverkraftHero

HoverkraftProjectCard

• In dark mode primary and neutral accent have the same style. Make them different.
  

• In light mode, primary accent does not look like primary, neutral accent rendering is bad. Fix that
  

Constraints

Ensure rendering respect accessibility constraints, and have an awesome look and feel in these cobined context

• light /dark mode</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes feat: UI enhancements #36

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