frontend: add Create-profile setup screen for brand-new accounts

LoginGate now shows CreateProfile (display name only) instead of App when
an authenticated session has no provisioned geniusrun profile yet, backed
by the new POST /api/setup endpoint and session/me's has_profile flag.

frontend/src/CreateProfile.css

@@ -0,0 +1,43 @@
+.create-profile {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  height: 100vh;
+  gap: 1rem;
+  text-align: center;
+}
+
+.create-profile form {
+  display: flex;
+  flex-direction: column;
+  gap: 0.75rem;
+  width: 100%;
+  max-width: 320px;
+}
+
+.create-profile input {
+  padding: 0.6rem 0.8rem;
+  font-size: 1rem;
+  border-radius: 0.5rem;
+  border: 1px solid #ccc;
+}
+
+.create-profile button {
+  padding: 0.6rem 0.8rem;
+  font-size: 1rem;
+  border-radius: 0.5rem;
+  border: none;
+  background: #3b82f6;
+  color: white;
+  cursor: pointer;
+}
+
+.create-profile button:disabled {
+  opacity: 0.6;
+  cursor: not-allowed;
+}
+
+.create-profile-error {
+  color: #ef4444;
+}

frontend/src/CreateProfile.tsx

@@ -0,0 +1,52 @@
+import { useState } from "react";
+import { api } from "./api/client";
+import "./CreateProfile.css";
+
+// Shown once, right after a brand-new OIDC login, before the account has a
+// geniusrun profile at all. The only thing asked for is a display name --
+// Garmin credentials and every other tunable are filled in afterward via
+// the existing Profile screen, same as a fresh single-user install today.
+export function CreateProfile({ onCreated }: { onCreated: (displayName: string) => void }) {
+  const [displayName, setDisplayName] = useState("");
+  const [submitting, setSubmitting] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  const handleSubmit = async (e: React.FormEvent) => {
+    e.preventDefault();
+    const trimmed = displayName.trim();
+    if (!trimmed) {
+      setError("Please enter a display name.");
+      return;
+    }
+    setSubmitting(true);
+    setError(null);
+    try {
+      const result = await api.setup(trimmed);
+      onCreated(result.display_name);
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Something went wrong, please try again.");
+      setSubmitting(false);
+    }
+  };
+
+  return (
+    <div className="create-profile">
+      <h1>🧞‍♀️ Welcome to geniusrun</h1>
+      <p>Let's set up your profile. You can add your Garmin account afterward.</p>
+      <form onSubmit={handleSubmit}>
+        <input
+          type="text"
+          placeholder="Display name"
+          value={displayName}
+          onChange={(e) => setDisplayName(e.target.value)}
+          disabled={submitting}
+          autoFocus
+        />
+        {error && <p className="create-profile-error">{error}</p>}
+        <button type="submit" disabled={submitting}>
+          {submitting ? "Creating…" : "Continue"}
+        </button>
+      </form>
+    </div>
+  );
+}

frontend/src/LoginGate.tsx

@@ -2,6 +2,7 @@ import { useEffect, useState } from "react";
 import { api, BASE_URL } from "./api/client";
 import "./LoginGate.css";
 import App from "./App";
+import { CreateProfile } from "./CreateProfile";
 import type { SessionInfo } from "./types/api";
 
 type Status = "loading" | "authenticated" | "unauthenticated";
@@ -13,8 +14,10 @@ const AUTH_ERROR_MESSAGES: Record<string, string> = {
 
 // Wraps App: on mount, asks the backend whether this browser already has a
 // valid session (GET /api/session/me). geniusrun has no anonymous view, so
-// this is the only fork in the whole frontend between "show the login
+// this is the first fork -- "show the login screen" vs "show the app." A
-// screen" and "show the app."
+// second fork, once authenticated, is whether the session's account has a
+// provisioned profile yet (session.has_profile) -- a brand-new OIDC login
+// sees CreateProfile instead of App until it submits one.
 export function LoginGate() {
   const [status, setStatus] = useState<Status>("loading");
   const [session, setSession] = useState<SessionInfo | null>(null);
@@ -46,5 +49,13 @@ export function LoginGate() {
     );
   }
 
+  if (!session!.has_profile) {
+    return (
+      <CreateProfile
+        onCreated={(displayName) => setSession((s) => (s ? { ...s, has_profile: true, display_name: displayName } : s))}
+      />
+    );
+  }
+
   return <App session={session!} />;
 }

frontend/src/api/client.ts

@@ -46,6 +46,11 @@ export const api = {
   // browser navigation. Logout must POST (see server.go's route), which an
   // <a href> can't do, hence the form.
   getSessionInfo: () => request<SessionInfo>("/api/session/me"),
+  setup: (displayName: string) =>
+    request<{ user_id: number; display_name: string }>("/api/setup", {
+      method: "POST",
+      body: JSON.stringify({ display_name: displayName }),
+    }),
 
   // Auth
   login: () => request<AuthResponse>("/api/auth/login", { method: "POST" }),

frontend/src/types/api.ts

@@ -189,6 +189,8 @@ export interface AuthResponse {
 export interface SessionInfo {
   name: string;
   email: string;
+  has_profile: boolean;
+  display_name?: string;
 }
 
 export interface DetailFillProgress {