settings: add nav visibility prefs and per-user Strava credentials

- user_prefs table in db.py with get/set helpers
- GET/PUT /api/me/prefs endpoints for bulk pref management
- GET/PUT/DELETE /api/me/strava-credentials; PUT preserves existing
  secret when client_secret field is left blank
- _strava_creds() helper resolves per-user → instance fallback across
  all five Strava endpoints
- Settings page: Navigation card (hide Feed/Community/About toggles)
  and Strava credentials card
- Base.astro: ids on feed/community/about nav links; applies
  nav_hide_* prefs after login

site/src/layouts/Base.astro

@@ -166,7 +166,7 @@ try {
         <div class="nav-links flex items-center gap-5 overflow-x-auto flex-1 min-w-0">
           <!-- Feed tab: only shown for multi-user (more than one shard) -->
           {!singleHandle && (
-            <a href={baseUrl} class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">Feed</a>
+            <a id="nav-feed" href={baseUrl} class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">Feed</a>
           )}
           <!-- Single-user: static handle link. Multi-user: populated by user-widget script. -->
           {singleHandle
@@ -177,7 +177,7 @@ try {
           <a id="nav-stats"   href={singleHandle ? `${baseUrl}u/${singleHandle}/stats/`   : `${baseUrl}stats/`}   data-user-path="stats/"   class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">Stats</a>
           <a id="nav-athlete" href={singleHandle ? `${baseUrl}u/${singleHandle}/athlete/` : `${baseUrl}athlete/`} data-user-path="athlete/" class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">Athlete</a>
           {!singleHandle && (
-            <a href={`${baseUrl}community/`} class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">Community</a>
+            <a id="nav-community" href={`${baseUrl}community/`} class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">Community</a>
           )}
           {mobileApp && (
             <a id="nav-record" href={singleHandle ? `${baseUrl}u/${singleHandle}/record/` : `${baseUrl}record/`} data-user-path="record/" class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">Record</a>
@@ -185,7 +185,7 @@ try {
           {mobileApp && (
             <a href={`${baseUrl}convert/`} class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">Convert</a>
           )}
-          <a href={`${baseUrl}about/`} class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">About</a>
+          <a id="nav-about" href={`${baseUrl}about/`} class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">About</a>
         </div>
       )}
 
@@ -511,6 +511,25 @@ try {
           const chk = document.getElementById('upload-keep-original');
           if (chk && user.store_originals_default) chk.checked = true;
 
+          // Apply nav visibility prefs
+          try {
+            const pr = await fetch('/api/me/prefs', { credentials: 'include' });
+            if (pr.ok) {
+              const prefs = await pr.json();
+              const navHideMap: Record<string, string> = {
+                'nav_hide_feed':      'nav-feed',
+                'nav_hide_community': 'nav-community',
+                'nav_hide_about':     'nav-about',
+              };
+              for (const [key, elId] of Object.entries(navHideMap)) {
+                if (prefs[key] === 'true') {
+                  const el = document.getElementById(elId);
+                  if (el) el.style.display = 'none';
+                }
+              }
+            }
+          } catch (_) {}
+
           // Admin: show admin link and poll for active jobs
           if (user.is_admin) {
             const adminLink = document.getElementById('nav-admin');