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

apps/client/src/components/layouts/global/app-header.tsx

@@ -1,6 +1,7 @@
 import {
   Box,
   Group,
+  Text,
   Tooltip,
 } from "@mantine/core";
 import classes from "./app-header.module.css";
@@ -76,7 +77,20 @@ export function AppHeader() {
             </Box>
           </Link>
 
-          <Group ml={50} gap={5} className={classes.links} visibleFrom="sm">
+          <Tooltip label={t("Version")}>
+            <Text
+              size="xs"
+              c="dimmed"
+              lh={1}
+              ml="md"
+              visibleFrom="sm"
+              style={{ userSelect: "text", whiteSpace: "nowrap" }}
+            >
+              {APP_VERSION}
+            </Text>
+          </Tooltip>
+
+          <Group ml="xl" gap={5} className={classes.links} visibleFrom="sm">
             {items}
           </Group>
         </Group>