Refactor web build process and update documentation

- Removed Node.js build artifacts from .gitignore and adjusted Makefile to reflect changes in web UI build process, now using server-rendered Go templates instead of React.
- Updated README to clarify the new web UI architecture and output formats, emphasizing the removal of the Node.js build step.
- Added a command to set the number of frames per render task in manager configuration, enhancing user control over rendering settings.
- Improved Gitea workflow by removing unnecessary npm install step, streamlining the CI process.

web/static/login.js

@@ -0,0 +1,65 @@
+(function () {
+  const loginForm = document.getElementById("login-form");
+  const registerForm = document.getElementById("register-form");
+  const errorEl = document.getElementById("auth-error");
+
+  function setError(msg) {
+    if (!errorEl) return;
+    if (!msg) {
+      errorEl.classList.add("hidden");
+      errorEl.textContent = "";
+      return;
+    }
+    errorEl.textContent = msg;
+    errorEl.classList.remove("hidden");
+  }
+
+  async function postJSON(url, payload) {
+    const res = await fetch(url, {
+      method: "POST",
+      credentials: "include",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify(payload),
+    });
+    const body = await res.json().catch(() => ({}));
+    if (!res.ok) {
+      throw new Error(body.error || "Request failed");
+    }
+    return body;
+  }
+
+  if (loginForm) {
+    loginForm.addEventListener("submit", async (e) => {
+      e.preventDefault();
+      setError("");
+      const fd = new FormData(loginForm);
+      try {
+        await postJSON("/api/auth/local/login", {
+          username: fd.get("username"),
+          password: fd.get("password"),
+        });
+        window.location.href = "/jobs";
+      } catch (err) {
+        setError(err.message);
+      }
+    });
+  }
+
+  if (registerForm) {
+    registerForm.addEventListener("submit", async (e) => {
+      e.preventDefault();
+      setError("");
+      const fd = new FormData(registerForm);
+      try {
+        await postJSON("/api/auth/local/register", {
+          name: fd.get("name"),
+          email: fd.get("email"),
+          password: fd.get("password"),
+        });
+        window.location.href = "/jobs";
+      } catch (err) {
+        setError(err.message);
+      }
+    });
+  }
+})();