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/templates/login.html

@@ -0,0 +1,41 @@
+{{ define "page_login" }}
+<section class="card narrow">
+  <h1>Sign in to JiggaBlend</h1>
+  {{ $view := .Data }}
+  {{ if index $view "error" }}
+  <div class="alert error">Login error: {{ index $view "error" }}</div>
+  {{ end }}
+
+  <div class="auth-grid">
+    {{ if index $view "google_enabled" }}
+    <a class="btn" href="/api/auth/google/login">Continue with Google</a>
+    {{ end }}
+    {{ if index $view "discord_enabled" }}
+    <a class="btn" href="/api/auth/discord/login">Continue with Discord</a>
+    {{ end }}
+  </div>
+
+  {{ if index $view "local_enabled" }}
+  <div class="split">
+    <form id="login-form" class="stack">
+      <h2>Local Login</h2>
+      <label>Email or Username<input type="text" name="username" required></label>
+      <label>Password<input type="password" name="password" required></label>
+      <button type="submit" class="btn primary">Login</button>
+    </form>
+
+    <form id="register-form" class="stack">
+      <h2>Register</h2>
+      <label>Name<input type="text" name="name" required></label>
+      <label>Email<input type="email" name="email" required></label>
+      <label>Password<input type="password" name="password" minlength="8" required></label>
+      <button type="submit" class="btn">Register</button>
+    </form>
+  </div>
+  {{ else }}
+  <p>Local authentication is disabled.</p>
+  {{ end }}
+
+  <p id="auth-error" class="alert error hidden"></p>
+</section>
+{{ end }}