Improve contact page to emphasize advisor, platform seats, and content collaboration

[ryanbaumann]

Motivation

• Make the Contact page more user-facing and actionable by shifting away from raw email copy toward clear collaboration paths (advisor work, additional platform seats, and content collaboration).
• Emphasize the AI-native developer experience and agent-driven, natural-language product interactions as the primary areas of engagement and growth the site should surface.

Description

• Rewrote the contact section HTML in portfolio/build.mjs to use a new heading, lede, and three prompt cards for Advisor work, Platform growth, and Content collaboration, and added a more specific message placeholder for the form.
• Added lightweight card styling for the new .contact-prompts cluster in portfolio/style.css that reuses existing design tokens and follows the repo's design guidance.
• Updated CHANGELOG.md to record the Contact page copy change.

Testing

• Ran the site build with cd portfolio && node build.mjs, which completed successfully and reported the pages built.
• Ran the gateway unit tests with cd gateway && npm test, which passed (all tests green).
• Attempted a Playwright-based screenshot command but it could not run in this environment because Playwright browser binaries are not installed, so visual screenshot validation was skipped.

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Codex Task