Improve how hero headline hyphenated compound words render

[juliasilge]

A followup to #384

The homepage headline ("The data science IDE. Human-driven, AI-assisted.") wrapped awkwardly at most widths. Because a hyphen is a valid line-break point, the browser would split hyphenated compounds mid-word (e.g. "AI-" / "assisted"), and the break landed inconsistently.

This PR:

• Forces the line break at the sentence boundary with <br>, so the H1 reads as two clean lines: "The data science IDE." / "Human-driven, AI-assisted."
• Wraps "Human-driven," and "AI-assisted." in .nowrap spans (with a new white-space: nowrap rule scoped to .index-section h1) so those compounds never split mid-word, including when the second sentence wraps on narrow mobile screens.

The H1 sits above the profile-specific content blocks, so this applies to both the public and Workbench builds.

Here's what we'll have after this change for big screens:

For little screens:

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[cindyytong]

Thank you!!