fix(server): parametrise named restore point query to prevent SQL injection

ServerNode.create_restore_point interpolated the user-supplied "value"
field directly into a SQL string with str.format(), so an authenticated
pgAdmin user could inject additional statements through that endpoint.
The injection ran with the user's own database role -- so it did not
cross a privilege boundary and granted no capability the role does not
already have via the Query Tool -- but it bypassed the documented SQL-
execution path and any application-layer controls a deployment may
have built around the Query Tool.

Pass the name as a bound parameter, and qualify the function with
pg_catalog so a non-default search_path on the connection cannot
redirect the call to a shadow definition.

Add a regression test that mocks the driver and asserts the call
arrives as ("SELECT pg_catalog.pg_create_restore_point(%s);", (name,))
with no payload spliced into the SQL text, plus defence-in-depth
assertions that the SQL string contains neither pg_sleep nor the PoC's
closing-quote signature, so a future refactor that reintroduces string
formatting is caught.

Reported by: Geo <cve@sageby.com>
Reviewed by: Kundan Sable <kundan.sable@enterprisedb.com>