Use the git commit hash as the app version

- Spec header, status pill and footer now document '<env> @ <hash>'
  instead of invented release numbers
- Backend settings expose GIT_COMMIT_HASH / APP_ENV / APP_VERSION,
  mirroring the original app
- Frontend bakes the short hash in at build time and shows it in the
  top bar

frontend/src/components/AppShell.tsx

@@ -2,6 +2,7 @@ import { LogOut } from "lucide-react";
 import { Link, NavLink, Outlet } from "react-router-dom";
 
 import { cn } from "@/lib/cn";
+import { APP_VERSION } from "@/lib/version";
 import { useAuth } from "@/store/auth";
 
 const navItems = [
@@ -21,9 +22,6 @@ export function AppShell() {
             <span className="rounded bg-ctp-mauve px-2 py-1 font-mono text-xs font-bold tracking-wide text-ctp-crust">
               J621
             </span>
-            <span className="hidden text-[11px] font-medium uppercase tracking-[0.14em] text-ctp-overlay0 md:block">
-              Mocha Archive Terminal
-            </span>
           </Link>
 
           <nav className="flex items-center gap-1">
@@ -47,6 +45,12 @@ export function AppShell() {
           </nav>
 
           <div className="ml-auto flex items-center gap-3">
+            <span
+              className="hidden font-mono text-[11px] text-ctp-overlay0 lg:block"
+              title="Running build"
+            >
+              {APP_VERSION}
+            </span>
             {user ? (
               <>
                 <div className="flex items-center gap-2">

frontend/src/lib/version.ts

@@ -0,0 +1,5 @@
+declare const __GIT_COMMIT_HASH__: string;
+
+export const GIT_COMMIT_HASH = __GIT_COMMIT_HASH__;
+export const APP_ENV = import.meta.env.DEV ? "dev" : "prod";
+export const APP_VERSION = `${APP_ENV} @ ${GIT_COMMIT_HASH}`;