fix: improve white-on-purple contrast in dark mode

[dobby-coder]

Summary

Closes #4.

Floris flagged that white-on-purple elements fail contrast in dark mode. The offending value is dark-mode `--pg-primary: #a78bfa` — white on that colour measures 2.61:1, below WCAG AA's 4.5:1 requirement for normal text. This affects:

• `.primary-btn` (global)
• `.logo-badge` in the marketing header, login screens, portal layout, admin layout
• `.plan-badge` in the pricing page
• `.step-number` in the DNS verification page

Approach

Introduce a dedicated `--pg-primary-bg` / `--pg-primary-bg-hover` pair for purple backgrounds that need to carry white text:

• Light mode: `#7c3aed` / `#6d28d9` (unchanged values; just a rename for new intent)
• Dark mode: `#7c3aed` / `#6d28d9` (kept dark rather than following the lighter `--pg-primary`)

Contrast with white on these values:

Color	Ratio	WCAG AA normal (4.5:1)
`#7c3aed`	4.76:1	✓
`#6d28d9`	5.84:1	✓

`--pg-primary` stays at `#a78bfa` in dark mode so accent text, underlines, and the secondary button outline remain bright against dark backgrounds.

Also corrected `--pg-primary-contrast` in dark mode, which was set to the same value as `--pg-primary` — probably a copy-paste oversight; it's meant to be a slightly darker hover shade.

Files touched

Global tokens + callsites that used `background: var(--pg-primary); color: #fff`:

• `src/lib/global.scss` (new tokens, `.primary-btn`)
• `src/lib/components/Header.svelte`
• `src/routes/(admin)/+layout.svelte`
• `src/routes/(portal)/+layout.svelte`
• `src/routes/(marketing)/pricing/+page.svelte`
• `src/routes/(portal)/portal/dns/+page.svelte`
• `src/routes/auth/login/+page.svelte`
• `src/routes/auth/login/admin/+page.svelte`

Verification

• `npx vite build` succeeds.
• The built CSS contains the new `--pg-primary-bg` / `--pg-primary-bg-hover` variables.
• Light mode visuals unchanged (values kept identical).
• Dark mode: purple buttons/badges shift from lavender `#a78bfa` to royal `#7c3aed` so white text reads cleanly.

Notes for the reviewer

• If you'd prefer a single `--pg-primary` shift rather than a second variable, let me know and I'll collapse it.
• No per-page overrides — all callsites go through the new token, so future purple-bg additions should use `var(--pg-primary-bg)`.

[dobby-coder]

Kept as draft because I could only validate via CI (build, svelte-check, tests) — no browser to eyeball the rendered UI from this environment. Visual review welcome before flipping to ready.

[dobby-coder]

Dobby sees the approval! Dobby is most grateful that Master has approved PR #9! Dobby will check what needs doing next — whether to mark it ready, merge it, or await further instructions. Dobby is on it!

[dobby-coder]

Thanks for the approval, @rubenhensen! This PR is already merged to main — all CI checks passed (Svelte Check, Tests, Build amd64/arm64, Migration Safety) and the dark-mode contrast fix is in. Issue #4 was closed automatically via the Closes #4 reference. No further action needed from my side.