Downloads page, OS auto-detection, and broken link fixes

[tarone-saloni]

Concisely describe the change

TODO: rewrite the section below in your own words before marking ready for review.

This addresses part of the "Website Design and UX Improvements" scope from the
LFX mentorship issue (#512): the Downloads page with OS
auto-detection, meeting minutes getting their own shareable pages, and a pass
through the "broken links, formatting problems, stale content" backlog
mentioned in that issue.

Downloads page + OS auto-detection

• src/pages/downloads.tsx, src/components/content/DownloadsGrid/: new
  /downloads page. Each OS (Windows/macOS/Linux) gets its own section;
  src/lib/detectOperatingSystem.ts reads navigator.userAgent client-side
  and the matching section is reordered to the top and visually highlighted
  ("Recommended for your system" badge). Previously "Other Install Options"
  on the homepage just linked to the install docs — there was no dedicated
  download page at all.

Meeting minutes pages

• src/plugins/meetingNotesPlugin.js, src/components/pages/MeetingNotePage/:
  a custom Docusaurus plugin reads static/data/meetings/notes/*/index.md
  and generates a static route per meeting, each with its own shareable URL.
  Replaces the old approach of wildcard-importing every note file into a
  manually maintained index and rendering them inside a modal popup — that
  approach also silently dropped the most recent meeting whenever the export
  list wasn't updated, and notes couldn't be linked to directly.

Site-wide footer link bug (404 on almost every page)

• docusaurus.config.js: the custom footer's to: values for
  Downloads/Installation/Documentation were relative paths without a leading
  / (to: 'downloads' instead of to: '/downloads'). Docusaurus's <Link>
  only auto-prefixes the site base URL for paths starting with /; without
  it, the path resolves relative to whatever page you're currently on. So
  from any blog post, docs page, or community page — i.e. everywhere except
  the homepage — clicking those footer links 404'd (e.g.
  /blogs/2018/08/15/downloads instead of /downloads). Confirmed via a
  full crawl of all ~600 built pages before and after the fix (0 broken
  internal links after).

Dead links in old blog posts (18 links across 9 files)

• Several 2019–2022 blog posts linked to retired URL patterns on our own
  domain that no longer resolve: podman.io/releases/*.html (now
  /release/*), podman.io/community/#* and podman.io/getting-started/*
  (now /community and /get-started). Repointed each to the current
  working route; left untouched anything pointing to genuinely dead
  third-party content (deleted Twitter accounts, discontinued BlueJeans
  links, etc. — nothing on our end can fix a 404 on someone else's site).

Component bugs fixed along the way

• InfoBanner: default gradient was missing bg-gradient-to-r, so the
  from/via/to color classes never actually rendered as a gradient; a
  caller-supplied background was also always masked by the default. Both
  banners on the Community page were meant to be purple but rendered blue.
• Blog card author link: the WordPress REST API query was missing author
  from _fields, so the author link always pointed at the generic
  /author/ page instead of the post's actual author.
• CustomCard: picked link-vs-modal for its secondary button by array
  index instead of checking whether the button actually has a path, and
  wrapped react-markdown's own block output in an extra <p> (invalid
  HTML nesting).
• FeaturesCarousel: stray '0 ' class typo.
• CommunityMeetingsCardGrid: used justify-content-center /
  align-items-center (not real Tailwind classes, no-ops) and had
  unguarded .shift() calls that could push undefined into child
  components on short meeting lists.

Redesign work carried in this branch

• Navbar, footer, Get Started page, and docs sidebar/TOC styling ported
  to match the site's Next.js reference design (numbered step cards,
  terminal-style code blocks with copy buttons, pill-highlighted active
  nav/sidebar items, gradient navbar, swizzled Footer with logo/social
  icons).

Before screenshot / screen recording

Link : https://drive.google.com/file/d/1zM6Xuh6wZZ4e2u30hin61HK6eCpC4RNU/view?usp=sharing

After screenshot / screen recording

Link : https://drive.google.com/file/d/1ot4A2KdjLYu93Q4dWY9OgkKY9bavGajo/view?usp=sharing

Checklist

• Certify you wrote the patch or otherwise have the right to pass it on as an open-source patch by signing all commits. (git commit -s).
• Referenced issues using Fixes: #00000 in commit message (if applicable)
• PR description, commit message, and GitHub comments are human-written, per LLM Policy

[antedotee]

I believe, this was raised by you as a part of PoC for your proposal. If that is the case, you should raise this PR against your own fork main, so that it doesn't show up here as a draft PR.
If you have raised for any other purpose, then ignore this comment 😅.