feat(outbound): add HTTPS CHECK constraint on outbound_connections.url

Defense-in-depth per code review. DTO layer already validates HTTPS at save
time; this DB-level check guards against future code paths that might bypass
the DTO validator. Mustache template variables in the URL (e.g., {{env.slug}})
remain valid since only the scheme prefix is constrained.

cameleer-server-app/src/main/resources/db/migration/V11__outbound_connections.sql

@@ -10,7 +10,7 @@ CREATE TABLE outbound_connections (
   tenant_id                 varchar(64) NOT NULL,
   name                      varchar(100) NOT NULL,
   description               text,
-  url                       text NOT NULL,
+  url                       text NOT NULL CHECK (url ~ '^https://'),
   method                    outbound_method_enum NOT NULL,
   default_headers           jsonb NOT NULL DEFAULT '{}',
   default_body_tmpl         text,