feat(settings): public_base_url field in general settings UI

roundtable/settings/routes.py

@@ -90,6 +90,8 @@ async def save_general():
     form = await request.form
     async with current_app.db_sessionmaker() as db:
         async with db.begin():
+            await set_setting(db, "general.public_base_url",
+                              (form.get("general.public_base_url", "") or "").strip())
             await set_setting(db, "session.lifetime_hours",
                               int(form.get("session.lifetime_hours", 8)))
             await set_setting(db, "data.retention_days",

roundtable/templates/settings/general.html

@@ -9,6 +9,18 @@
 <div class="card" style="max-width:640px;">
   <h2 class="section-title" style="margin-bottom:1.25rem;">General</h2>
 
+  <div class="form-group">
+    <label>Public base URL</label>
+    <input type="text" name="general.public_base_url"
+           value="{{ settings['general.public_base_url'] }}"
+           placeholder="https://monitor.example.com">
+    <div style="font-size:0.78rem;color:var(--text-muted);margin-top:0.25rem;">
+      External URL where this Roundtable instance is reachable from the outside.
+      Leave blank to use whatever hostname you're currently browsing via.
+      Used by install scripts, share links, and alert notifications.
+    </div>
+  </div>
+
   <div class="form-group">
     <label>Session lifetime <span style="color:var(--text-muted);font-size:0.8rem;">(hours)</span></label>
     <input type="number" name="session.lifetime_hours" min="1" max="720"