feat: bake version into binary and display in UI sidebar

- Inject VERSION via ldflags (-X main=web.Version=) and git short SHA
- Add /api/version endpoint returning {version, commit}
- Display version in Layout sidebar footer (v0.1.6 · 8cfd405)
- Add AGENTS.md section documenting SemVer policy and bump-before-push rule
- Bump VERSION 0.1.5 -> 0.1.6 in Makefile

web/src/api.ts

@@ -65,6 +65,11 @@ export interface SystemStatus {
   services: ServiceStatus[];
 }
 
+export interface VersionInfo {
+  version: string;
+  commit: string;
+}
+
 export class ApiError extends Error {
   status: number;
   constructor(status: number, message: string) {
@@ -104,6 +109,7 @@ export const api = {
   apply: () => request<{ results: { module: string; applied: boolean; error?: string }[] }>("POST", "/apply"),
   applyLog: () => request<{ entries: ApplyLogEntry[] }>("GET", "/apply/log"),
   systemStatus: () => request<SystemStatus>("GET", "/system/status"),
+  version: () => request<VersionInfo>("GET", "/version"),
 
   // samba
   listShares: () => request<{ shares: SambaShare[] | null }>("GET", "/samba/shares/"),

web/src/components/Layout.tsx

@@ -1,5 +1,6 @@
+import { useEffect, useState } from "react";
 import { NavLink, Outlet, useNavigate } from "react-router-dom";
-import { api } from "../api";
+import { api, VersionInfo } from "../api";
 import DirtyBanner from "./DirtyBanner";
 
 const navItems = [
@@ -13,6 +14,11 @@ const navItems = [
 
 export default function Layout({ username, onLogout }: { username: string; onLogout: () => void }) {
   const navigate = useNavigate();
+  const [version, setVersion] = useState<VersionInfo | null>(null);
+
+  useEffect(() => {
+    api.version().then(setVersion).catch(() => {});
+  }, []);
 
   async function handleLogout() {
     await api.logout();
@@ -47,6 +53,9 @@ export default function Layout({ username, onLogout }: { username: string; onLog
           <button className="btn-ghost w-full" onClick={handleLogout}>
             Cerrar sesión
           </button>
+          <div className="mt-2 border-t border-slate-800 pt-2 text-center font-mono text-xs text-slate-600">
+            v{version?.version ?? "dev"}{version?.commit && ` · ${version.commit}`}
+          </div>
         </div>
       </aside>
       <main className="flex-1">