feat(client): show git-describe version next to the brand logo

Display the app version (output of `git describe --tags`) in the header
beside the gitmost logo: a clean tag renders as `vX.Y.Z`, otherwise the
tag plus commits-since and short hash (e.g. v0.90.1-56-g25975acd).

- vite.config.ts: resolve APP_VERSION from env (Docker/CI) -> git describe
  (local) -> package.json version fallback
- app-header.tsx: render APP_VERSION after the brand block (ml="md"),
  nudge the Home nav group (ml={50} -> "xl")
- Dockerfile: accept APP_VERSION build-arg in the builder stage (.git is
  excluded from the build context)
- CI: pass APP_VERSION build-arg — release.yml uses the tag, develop.yml
  computes git describe with fetch-depth: 0
- nx.json: add APP_VERSION to the build target inputs so the cache
  invalidates when the version changes

Dockerfile

@@ -10,6 +10,9 @@ WORKDIR /app
 COPY . .
 
 RUN pnpm install --frozen-lockfile
+# Version string shown in the UI (computed outside Docker because .git is not in the build context).
+ARG APP_VERSION=""
+ENV APP_VERSION=$APP_VERSION
 RUN pnpm build
 
 FROM base AS installer