refactor(store): single account name on users; rename profile/laps tables

users.display_name becomes users.name and is now the only human-facing
name -- profiles.name is dropped (it duplicated the account name; the
Profile page's Name field now edits users.name through PUT /api/profile,
which carries Name alongside the profiles columns). The profile table
becomes profiles and laps becomes activity_laps, homogeneous with
activity_samples. Onboarding pre-fills the display name from the OIDC
claim's name.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/LoginGate.tsx

@@ -84,6 +84,7 @@ export function LoginGate() {
   if (!session!.has_profile) {
     return (
       <OnboardingWizard
+        defaultName={session!.name}
         onCreated={(displayName) => setSession((s) => (s ? { ...s, has_profile: true, display_name: displayName } : s))}
       />
     );

frontend/src/OnboardingWizard.tsx

@@ -15,9 +15,17 @@ type Step = "name" | "garmin";
 // database -- there's no half-created account to clean up or re-prompt
 // for later, so there's deliberately no "Log out" escape hatch anywhere in
 // this flow: closing the tab *is* the escape hatch.
-export function OnboardingWizard({ onCreated }: { onCreated: (displayName: string) => void }) {
+// defaultName pre-fills the display-name field with the OIDC claim's name --
+// most people keep it, and a single ✓ click through is nicer than retyping.
+export function OnboardingWizard({
+  onCreated,
+  defaultName = "",
+}: {
+  onCreated: (displayName: string) => void;
+  defaultName?: string;
+}) {
   const [step, setStep] = useState<Step>("name");
-  const [displayName, setDisplayName] = useState("");
+  const [displayName, setDisplayName] = useState(defaultName);
   const [email, setEmail] = useState("");
   const [password, setPassword] = useState("");
   const [code, setCode] = useState("");