Add public feed, admin area, self-registration, visibility & hashtags

- Public feed (/) with infinite scroll via Intersection Observer
- Self-registration (/register)
- Admin area (/admin/entries, /admin/users) with user management
- journal_entries: visibility (public/private) + hashtags fields
- users: is_admin flag
- DB schema updated (recreate DB to apply)
- CI: run go test via docker run (golang:1.25-alpine) — fixes 'go not found'

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/api/templates/public.html

@@ -0,0 +1,72 @@
+{{define "title"}}Journal — Öffentliche Einträge{{end}}
+
+{{define "content"}}
+<main class="container">
+  <nav>
+    <strong>Journal</strong>
+    <a href="/login">Anmelden</a>
+  </nav>
+
+  <div id="feed">
+    {{template "feed_items" .}}
+  </div>
+</main>
+{{end}}
+
+{{define "feed_items"}}
+{{range .Entries}}
+<article class="entry-card">
+  <header>
+    <small>{{.EntryDate}} · {{.EntryTime}}</small>
+    {{if .Title}}<strong> · {{.Title}}</strong>{{end}}
+  </header>
+  {{if .Description}}<p>{{.Description}}</p>{{end}}
+  {{if .Images}}
+  <div class="entry-images">
+    {{range .Images}}
+    <a href="/uploads/{{.Filename}}" target="_blank">
+      <img src="/uploads/{{.Filename}}" alt="{{.OriginalName}}" class="thumb">
+    </a>
+    {{end}}
+  </div>
+  {{end}}
+  {{if .Hashtags}}
+  <footer class="hashtags">
+    {{range .Hashtags}}<span class="tag">#{{.}}</span> {{end}}
+  </footer>
+  {{end}}
+</article>
+{{else}}
+<p><small>// Noch keine öffentlichen Einträge</small></p>
+{{end}}
+{{if .HasMore}}
+<div id="sentinel" data-offset="{{.Offset}}"></div>
+{{end}}
+{{end}}
+
+{{define "scripts"}}
+<script>
+(function() {
+  const sentinel = document.getElementById('sentinel');
+  if (!sentinel) return;
+  const obs = new IntersectionObserver(function(entries) {
+    if (!entries[0].isIntersecting) return;
+    obs.disconnect();
+    const offset = sentinel.dataset.offset;
+    fetch('/feed?offset=' + offset)
+      .then(r => r.text())
+      .then(html => {
+        sentinel.remove();
+        const div = document.createElement('div');
+        div.innerHTML = html;
+        document.getElementById('feed').append(...div.childNodes);
+        const next = document.getElementById('sentinel');
+        if (next) obs.observe(next);
+      });
+  });
+  obs.observe(sentinel);
+})();
+</script>
+{{end}}
+
+{{template "base" .}}