feat: prerelease workflow with major version support and version propagation

- Add docker-dev.yml: prerelease CI for dev branch with minor/major bump
  inputs; auto-continues in-flight major line via existing pre tags;
  publishes floating major-pre Docker tag (e.g. 2-pre)
- Rewrite docker.yml version-bump: tag-based versioning, manual bump
  inputs (auto/patch/minor/major), major guarded by confirm_major=MAJOR,
  auto-finalizes in-flight prereleases; publishes floating major tag (e.g. 2)
- Inject APP_VERSION build-arg through Dockerfile so the running container
  knows its real version instead of reading package.json
- Server reads APP_VERSION env in authService/adminService; exposes
  is_prerelease in app config and update-check response; prerelease builds
  compare against GitHub prerelease releases rather than latest stable
- Client stores isPrerelease from config; navbar shows amber version badge
  on prerelease builds (left of dark-mode toggle); GitHubPanel filters out
  prerelease releases unless the running build is itself a prerelease

client/src/components/Admin/GitHubPanel.tsx

@@ -6,7 +6,7 @@ import apiClient from '../../api/client'
 const REPO = 'mauriceboe/TREK'
 const PER_PAGE = 10
 
-export default function GitHubPanel() {
+export default function GitHubPanel({ isPrerelease = false }: { isPrerelease?: boolean }) {
   const { t, language } = useTranslation()
   const [releases, setReleases] = useState([])
   const [loading, setLoading] = useState(true)
@@ -273,7 +273,7 @@ export default function GitHubPanel() {
             <div className="absolute left-[11px] top-3 bottom-3 w-px" style={{ background: 'var(--border-primary)' }} />
 
             <div className="space-y-0">
-              {releases.map((release, idx) => {
+              {(isPrerelease ? releases : releases.filter((r: any) => !r.prerelease)).map((release, idx) => {
                 const isLatest = idx === 0
                 const isExpanded = expanded[release.id]