Give the guest setting somewhere to be changed

Reported: no Tools section in Settings. The setting existed in the database and
had no page, which from a person's side is indistinguishable from the feature
not existing.

get_settings_defaults SEEDS a setting. get_settings_cards (ADR-010) is what puts
it in the rail. Declaring only the first is a silent half-feature: nothing fails,
no test notices, and the switch is unreachable.

The page states the cost where the DECISION is made rather than in a document
nobody opens - turn it on and it says a guest-created link records no creator,
so the audit trail can say when and from where but never who.

Admin-only, like every other settings page, because this one decides whether an
unauthenticated caller may write to the site.

Also caught while wiring it: the card asked for a 'shield' icon, which is not in
the settings iconMap, so it would have rendered the fallback puzzle piece - the
glyph that reads as "nobody chose this". Uses wrench, matching Tech Tools.

The row still comes from `flask plugin upgrade-all`; the card appears either
way, and without the row the page loads empty.

plugins/tools/plugin.py

@@ -92,6 +92,28 @@ class ToolsPlugin(BasePlugin):
             },
         ]
 
+    def get_settings_cards(self) -> List[dict]:
+        """A page for the one switch this plugin owns (ADR-010).
+
+        get_settings_defaults SEEDS the row; this is what gives somebody a place
+        to change it. Declaring only the first left the setting in the database
+        with no way to reach it, which is indistinguishable from the feature not
+        existing.
+        """
+        return [
+            {
+                'group': 'Tools',
+                'to': '/settings/secure-send',
+                # From the settings iconMap; an unknown key falls back to a
+                # puzzle piece, which reads as "nobody chose this".
+                'icon': 'wrench',
+                'title': 'Secure Send',
+                'description': 'Whether people without an account can create '
+                               'one-view password links',
+                'position': 60,
+            },
+        ]
+
     def get_navigation_items(self) -> List[dict]:
         return [
             {