feat(donate): balance PayPal and Ghost Keys CTAs

[sanity]

Problem

The donate page offered two ways to give, but they had wildly unequal visual weight:

1. PayPal — a full-size ## Donate heading + a filled primary button (.funding-donate-button).
2. Ghost Keys (card via Stripe) — no button at all, just a smaller greyed heading and a muted grey paragraph with an inline text link. .funding-ghost-keys deliberately shrank the heading (1.15rem, #64748b) and paragraph (0.95rem, #64748b).

This was intentional in a prior PR (understated Ghost Keys treatment), but the direction is being reversed: both are legitimate, genuinely different ways to donate, and should read as an equal choice, not a primary option and an afterthought.

Approach

Gave the card option the same visual treatment as PayPal, reusing existing patterns rather than inventing new ones:

• Matching heading style for both (## Donate via PayPal / ## Donate via card), same size/color in both themes.
• A real button for the card option using .funding-donate-button — the same class already used for Ghost Key CTAs on /ghostkey/, so no new button style was introduced. Links to /ghostkey/create/, the actual entry point used elsewhere on the site.
• A one-line note under both buttons (.gk-cta-note, already used on /ghostkey/), rather than a caption under only one — this keeps the fine print an equal-weight explainer on each side instead of a marker for the "lesser" option.
• Stripped .funding-ghost-keys's heading/paragraph color and font-size overrides; kept only the top divider that visually separates the two options.

Deliberately avoided: urgency, scarcity, pre-selecting one option, or guilt-framed copy on either side. Neither option is styled as the "recommended" or "default" choice.

funding-ghost-keys is only referenced in donate/_index.md (checked via grep before editing its rules), so this doesn't affect any other page.

Testing

Built with hugo --quiet (clean, no warnings/errors). Screenshotted and measured with Playwright at desktop (1280x900) and mobile (390x844), both light and dark color schemes, before and after.

Before (live site, desktop):

• PayPal: heading 25.2px tall (1.4rem, #1a1a2e), button 195x52
• Ghost Keys: heading 20.7px tall (1.15rem, #64748b), no button, plain paragraph 79.8px tall

After (this branch, desktop, both themes):

• PayPal heading: 22.4px font-size, rgb(26,26,46) light / rgb(232,232,232) dark
• Card heading: 22.4px font-size, same colors — identical to PayPal
• PayPal button: 195x52, rgb(0,102,204) background, 16px font
• Card button: 177x52 (width differs only because "Donate via card" vs "Donate via PayPal" is a different label length), same background, height, and font-size
• Both notes: 14.4px font-size, same color

Verified visually in all 4 combinations (desktop/mobile x light/dark) by reading the rendered screenshots, not just the numbers.

Closes the visual-parity request from Ian.

[AI-assisted - Claude]

[sanity]

Superseded by #117, which includes this PR's symmetry fix plus surfacing both CTAs above the fold (the scope grew after this PR was opened). Closing in favor of #117.

[AI-assisted - Claude]