feat(security): dedicated install flags decouple git_url/pip from security_level

Install via git URL and pip install are no longer gated by
security_level. Each surface gets a dedicated config.ini flag —
allow_git_url_install / allow_pip_install (both default false, secure
by default) — that fully REPLACES the security-level term for these two
features. The network-position invariant is retained: a non-local
listener stays denied regardless of the flags unless
network_mode = personal_cloud.

- New pure predicate is_dedicated_install_allowed() in
  common/manager_security (no config access; callers resolve config)
- Legacy endpoints /v2/customnode/install/git_url and .../pip switch
  from is_allowed_security_level('high+') to the flag gate; batch
  installs of unknown git URLs likewise (middle+ entry gate unchanged,
  unknown-pip 'block' stays unconditional; response shapes preserved)
- Config readers/writers (glob + legacy) parse and persist the flags;
  denial logs and frontend 403 messages name the responsible flag and
  note the non-local-listener requirement (network_mode=personal_cloud)
- No auto-seed from security_level — users previously on weak/normal-
  must opt in explicitly (see CHANGELOG migration notes; README
  documents the new contract)
- Update the pre-existing permissive E2E harness
  (start_comfyui_permissive.sh + test_e2e_legacy_real_ops.py) to the
  new contract: it now also sets allow_git_url_install /
  allow_pip_install = true, since security_level = normal- alone no
  longer opens the git_url/pip endpoints

Tests: predicate truth table proving security_level independence in
both directions, dual-reader config contract, security-level-matrix
freeze guards, legacy gate regression guards (121 unit), plus 22
real-server E2E tests incl. URL-form pip install with self-clean.

comfyui_manager/js/common.js

@@ -216,7 +216,7 @@ export async function install_pip(packages) {
 	});
 
 	if(res.status == 403) {
-		show_message('This action is not allowed with this security level configuration.');
+		show_message("To use this feature, set <code>allow_pip_install = true</code> in the [default] section of config.ini. This setting is independent of security_level.<BR>Note: if the ComfyUI listener is not local, <code>network_mode = personal_cloud</code> is also required.");
 		return;
 	}
 
@@ -251,7 +251,7 @@ export async function install_via_git_url(url, manager_dialog) {
 	});
 
 	if(res.status == 403) {
-		show_message('This action is not allowed with this security level configuration.');
+		show_message("To use this feature, set <code>allow_git_url_install = true</code> in the [default] section of config.ini. This setting is independent of security_level.<BR>Note: if the ComfyUI listener is not local, <code>network_mode = personal_cloud</code> is also required.");
 		return;
 	}