feat: add upload limits section to landing page

[dobby-coder]

Summary

Adds a prominent "generous file size limits" section to the marketing frontpage, communicating PostGuard's 5 GB-per-upload and 5 GB-per-2-weeks limits as a differentiator against competitors (who typically cap free encrypted file transfers at a few hundred MB).

What changed

• src/routes/(marketing)/+page.svelte
  • New <section class="limits"> placed directly below the hero — so it is the first thing a visitor sees after scrolling past the fold.
  • Stat card with large, primary-coloured number: 5 GB (per 2-week period).
  • Intro line that explicitly contrasts PostGuard against typical competitor caps.
  • Footnote reinforcing the "free, no account, always encrypted" pitch.
  • Responsive: collapses to a single column on ≤768 px.
• src/lib/locales/en.json and src/lib/locales/nl.json
  • New landing.limits.* keys for section copy, stat labels, descriptions, and footnote.
  • Dutch translations included.

Numbers

The 5 GB number is hardcoded in the template copy for now, matching issue #86. If #85 lands with that number sourced from env vars, we could wire VITE_MAX_UPLOAD_SIZE and VITE_ROLLING_LIMIT into this section in a follow-up — but the marketing copy is probably fine to keep decoupled, since the wording would need to change anyway if the numbers change.

How to verify

1. npm run dev
2. Visit http://localhost:5173/. The new section should appear immediately under the hero (scroll once).
3. Confirm the stat card shows 5 GB with the primary (blue) colour.
4. Toggle the language switcher to NL — all strings should translate (title, intro, stat descriptions, footnote).
5. Resize to a narrow viewport (<=768 px) — the stats should stack vertically.
6. Check both light and dark themes — card background / borders use the design system tokens so should look correct in both.

Status

Opening as draft because:

• Wording is a first cut; Ruben will almost certainly want to iterate on copy (tone, exact comparison framing, whether to add named-competitor callouts).
• Haven't rendered the exact design against any reference mocks (none linked in the issue).

Related

Closes #86.
Part of the upload-limits initiative — see also #85 (backend/env config) and #87 (in-app warnings/errors). Per the dobby coordination note, this PR is intentionally standalone (marketing copy only, no code dependency on #85 or cryptify#100).

[rubenhensen]

Competition does 3gb per month on a free tier. Not a few hundred megabytes. Change the wording to reflect this

[rubenhensen]

Superseded by #110 which combines this with #89 and #91.