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/glob/manager_core.py

@@ -1706,6 +1706,8 @@ def write_config():
         'network_mode': get_config()['network_mode'],
         'db_mode': get_config()['db_mode'],
         'verbose': get_config()['verbose'],
+        'allow_git_url_install': get_config()['allow_git_url_install'],
+        'allow_pip_install': get_config()['allow_pip_install'],
     }
 
     # Sanitize all string values to prevent CRLF injection attacks
@@ -1755,6 +1757,8 @@ def read_config():
                     'security_level': default_conf.get('security_level', SecurityLevel.NORMAL.value).lower(),
                     'db_mode': default_conf.get('db_mode', DBMode.CACHE.value).lower(),
                     'verbose': get_bool('verbose', False),
+                    'allow_git_url_install': get_bool('allow_git_url_install', False),
+                    'allow_pip_install': get_bool('allow_pip_install', False),
                }
 
     except Exception:
@@ -1783,6 +1787,8 @@ def read_config():
             'security_level': SecurityLevel.NORMAL.value,
             'db_mode': DBMode.CACHE.value,
             'verbose': False,
+            'allow_git_url_install': False,
+            'allow_pip_install': False,
         }