Tourmaline folded into pkgs monorepo, landing-ui improvements

Tourmaline into the monorepo. Moved from github.com/ewanc26/tourmaline to packages/tourmaline in the pkgs monorepo. Added @ewanc26/landing-ui and @ewanc26/noise-avatar as workspace dependencies. Removed .git, pnpm-lock.yaml, and pnpm-workspace.yaml from the package. Updated all GitHub links to point to the monorepo path (pkgs/tree/main/packages/tourmaline), including the MusicBrainz user agent string.

LandingLayout improvements. Added backdrop-blur to the sticky header (color-mix at 90% opacity + backdrop-filter: blur(8px)). Added optional navLinks prop for header navigation (Tourmaline passes About and GitHub). Made webVersion/cliVersion optional -- when absent, the version strip is hidden. Header right side now stacks nav links and version strip side by side.

LandingPage snippet props. Added optional heroAction and ctaAction snippet props. When provided, they replace the default hero CTA buttons and bottom CTA section respectively. Tourmaline passes its search form with Bluesky actor autocomplete as both heroAction and ctaAction. Made ctaHref, ctaLabel, ctaSub, and githubUrl optional so projects without a CLI pair (like Tourmaline) can omit them. Changed FeatureIcon type to import('svelte').Component | string to accept lucide icons from any version.

Fixed source URLs. footerSourceUrl in malachite-web, jasper-web, and bismuth-web now point to the correct subpath in the monorepo (pkgs/tree/main/packages/<name>). Opal was already correct.