feat(sidebar): hide gears whose agent reports them unavailable (#112)

filterGearsByAgentCapabilities is the framework's existing
capability-aware gear filter. Today it's only used by the Gears
settings page (`/settings/gears`) — so the **sidebar** still renders
HAProxy, Logs, Services, Certificates, etc. for an active box whose
agent doesn't run any of those gears. Clicking them lands the
operator on an empty page or a JSON-envelope error.

Run the same filter on the per-box integration list inside
InjectIntegrationStatus, so the sidebar reflects what the agent can
actually serve. Failures stay fail-open (an unreachable agent does
not strip the sidebar) by reusing the existing helper's contract.

Phase 2 slice of #112.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: sarg3nt

gearbox/internal/framework/handler/handler.go

@@ -524,6 +524,13 @@ func (h *Handler) InjectIntegrationStatus(next http.Handler) http.Handler {
 				next.ServeHTTP(w, r.WithContext(ctx))
 				return
 			}
+			// Filter the per-box gear list by the agent's probe table —
+			// if the agent reports a gear as unavailable, hide it from
+			// the sidebar entirely so the operator doesn't click into a
+			// page the box physically can't serve (issue #112). The
+			// filter fails OPEN: when the agent is unreachable the full
+			// list is preserved, matching the Gears-settings-page filter.
+			integrations = h.filterGearsByAgentCapabilities(activeBox.ID, integrations)
 			for _, i := range integrations {
 				status[i.Name] = i.Enabled
 				orderedIntegrations = append(orderedIntegrations, auth.SidebarIntegration{