Replace the header logo with the new Nebari Packs logos across the dashboard and all tracked packs

Summary

Swap the bundled Nebari mark for the new Nebari Packs logos (light and dark variants) in the docs header of this dashboard and every tracked pack's docs site, using the logo option added in @nebari/starlight 0.3.0. The logo image files are hosted here in software-pack-dashboard (site/public/), served from https://packs.nebari.dev/; each pack references them by absolute URL. Covers this repo plus the 14 pack repos listed in tracked-packs.yaml.

Motivation

• The packs portal has its own identity; pack docs currently render the general Nebari mark, which doesn't distinguish the packs ecosystem from the main project.
• All 15 sites already run @nebari/starlight ^0.3.0, which shipped the logo: { light, dark, alt } option specifically for this — the change is one config block per repo, no component overrides.
• Hosting the assets once in this repo keeps a single source of truth: a future logo refresh is one PR here instead of 15.
• All pack docs are served under packs.nebari.dev/<slug>/ in production, so referencing the dashboard-hosted files is a same-origin request.

Acceptance Criteria

• New nebari-packs-light.svg and nebari-packs-dark.svg added to site/public/ in this repo, served at https://packs.nebari.dev/nebari-packs-light.svg and .../nebari-packs-dark.svg after deploy
• This dashboard's site/astro.config.mjs passes logo: { light: '/nebari-packs-light.svg', dark: '/nebari-packs-dark.svg', alt: 'Nebari Packs' } to nebari() (local paths — same origin)
• Each of the 14 tracked pack repos (data-science-pack, llm-serving-pack, chat-pack, nebi-pack, lgtm-pack, superset-pack, rayserve-pack, mlflow-pack, provenance-collector-pack, pi-coding-agent-pack, skillsctl, langfuse-pack, nebari-frames, apps-pack) passes the same logo option with the absolute https://packs.nebari.dev/... URLs in its docs astro.config.mjs
• Existing logoHref/githubHref options are left unchanged by these PRs
• Both variants render correctly in light and dark theme on a built site (visual check on the dashboard plus at least one pack)
• The dashboard PR is merged and deployed before the pack PRs land, so the referenced asset URLs resolve

Out of Scope

• Designing the logo artwork itself — this issue starts when the light/dark SVGs are delivered by design
• Changes to @nebari/starlight — the logo option already exists in 0.3.0 and the packs are already on ^0.3.0 (fleet-wide header-links pass, e.g. nebari-dev/software-pack-dashboard#22)
• Favicons, footer branding, or any header changes beyond the logo image

Start with tracked-packs.yaml to confirm the 14 pack repositories, then inspect site/public/ and site/astro.config.mjs in this dashboard. Add the delivered light and dark SVG assets and compare the dashboard configuration with each pack's docs astro.config.mjs. Build the dashboard and at least one pack, then visually verify both theme variants and confirm the dashboard deploy precedes pack changes.