Split the fleet roster from per-endpoint reads, and stop offering controls nobody can use

Twelve endpoints routes shared one permission, which made a reasonable policy
impossible to express. A site that wants signed-out visitors to see live status
on a PC page had to hand them the entire fleet - including every logged-in
username on the floor - because the per-asset panels and the fleet-wide list
were gated on the same string.

endpoints.fleet now gates the list and the three dashboard routes.
endpoints.view keeps the per-asset reads: status, services, processes,
interfaces, events, command history.

The name is load-bearing. guest_grantable_permissions() opens any '.view' or
'.read' permission to the guest role, so calling this one 'endpoints.fleet'
rather than 'endpoints.fleetview' is what keeps the roster off the public
surface while per-asset telemetry stays grantable. Verified both ways.

Also: the services panel emitted Start/Stop row actions to every reader,
because row_actions_for() never consulted the caller. Clicking was always
refused server-side, so nothing was exploitable, but showing a read-only viewer
controls over a shop-floor PC is the wrong signal - and it stops being cosmetic
the moment a site grants that panel to guests.

That needed a contract addition rather than a local check: caller_holds() on
shopdb.api answers whether THIS caller holds a permission without refusing the
request, which is the complement to require_permission for a surface that
serves everyone but should only offer what the caller can act on. Guests are
included, since a signed-out visitor holds whatever the guest role was granted.
Reaching into shopdb.utils.authz instead would repeat the ADR-002 violation the
contract gate caught earlier in this branch. Contract 0.24.0 -> 0.25.0.

DEPLOYMENT: endpoints.fleet is a new permission. Run 'flask seed permissions'
and grant it to the roles that should keep seeing the Fleet page. Until then
that page is admin-only, since admins bypass every check - a safe direction,
but not an automatic one.

Full suite 2124 passed, naming and contract gates green, map and spec
regenerated.

shopdb/utils/authz.py

@@ -86,6 +86,32 @@ def guestholds(permission_name: str) -> bool:
     return any(p.name == permission_name for p in role.permissions)
 
 
+def caller_holds(permission_name: str) -> bool:
+    """Whether THIS caller holds a permission, without refusing the request.
+
+    require_permission answers the same question by returning 401/403. This
+    answers it in the body, for the case where a route serves everyone but
+    should only OFFER something to the callers who can use it.
+
+    The endpoints services panel is the example that prompted it: it emitted
+    Start/Stop buttons for every reader, because the emission never consulted
+    the caller. Clicking them 403s, so nothing was exploitable, but showing a
+    read-only viewer controls over a shop-floor PC is the wrong signal - and it
+    gets worse the moment a site grants that panel to guests.
+
+    Guests are included on purpose: a signed-out visitor holds whatever the
+    guest role was granted, so the answer must come from the same place
+    require_permission gets it.
+    """
+    user = currentuser()
+    if user is None:
+        return guestholds(permission_name)
+    try:
+        return bool(user.haspermission(permission_name))
+    except Exception:
+        return False
+
+
 def require_permission(permission_name: str):
     """Gate a route behind a single permission. Admin role bypasses.