Closes the C1 findings from issue #81 plus the round-3/4 follow-ups
on the read-only query path.
Both _attach_remote_extensions (rebuild path) and
_reattach_remote_extensions (query path) now apply the same hard
allowlists for extensions and token-env names, single-quote-escape
the URL, and split built-in vs community install. The CHANGELOG bullet
documents the full scope including the table_schema → table_catalog
fix that made the rebuild path a silent no-op for every connector.
New module src/orchestrator_security.py centralises the policy. Tests
in tests/test_orchestrator_remote_attach_security.py — 28/28 pass.
Refs #81.
