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

Add two boolean config.ini [default] flags — allow_git_url_install and
allow_pip_install (both default false) — that fully REPLACE the
security_level term on the legacy install surfaces:

- POST /v2/customnode/install/git_url (S-A) and
  POST /v2/customnode/install/pip (S-B) are now gated solely by their
  dedicated flag AND the retained network-position invariant
  (loopback listener OR network_mode=personal_cloud). security_level
  no longer affects these two surfaces in either direction.
- The batch unknown-URL branch (S-C) routes through the same predicate;
  the unknown-pip branch stays unconditionally blocked; the general
  middle+ batch entry gate is unchanged.
- New pure predicate is_dedicated_install_allowed() in
  common/manager_security.py (config-import-free; callers pass values
  from their own reader). Both config readers (glob + legacy) register
  the keys in read/write/fallback paths.
- Denial logs and frontend copy name the responsible flag instead of
  the misleading security_level guidance. Public listeners remain
  denied regardless of the flags (no exposure widening).
- README security policy updated: config keys documented, git-url/pip
  removed from the security_level risky table, and a dedicated-flags
  subsection (REPLACE semantics, network rule, batch behavior,
  restart-only activation, weak/normal- opt-in migration note).
- Migration: existing weak/normal- users must opt in via the new flags
  (CHANGELOG note; deliberate no auto-seed).

Includes the unit/config/guard test suites (88 tests): predicate truth
table, dual-reader config contract (missing/malformed keys read false,
round-trip, cache staleness), security_level-matrix freeze guards, and
suite-order-independent test stubs.

comfyui_manager/common/manager_security.py

@@ -83,6 +83,25 @@ def is_loopback(address):
         return False
 
 
+def is_dedicated_install_allowed(flag_value: bool, listen_address: str, network_mode: str) -> bool:
+    """P-direct predicate for the dedicated install flags (goal265-spec.md §1.2).
+
+    allowed iff flag AND (loopback listener OR network_mode == 'personal_cloud').
+
+    Gates the git-URL / standalone-pip install surfaces via the dedicated
+    ``allow_git_url_install`` / ``allow_pip_install`` config flags, fully
+    decoupled from ``security_level`` (REPLACE, not AND — spec §1.1 inv. 1).
+    The network-position term retains today's invariant that a public
+    (non-loopback, non-personal_cloud) listener stays denied regardless of
+    the flags (spec §1.1 inv. 2).
+
+    Pure function — NO config access; callers resolve ``flag_value`` and
+    ``network_mode`` through their own config reader and pass values in
+    (preserves common/ layering: this module must stay config-import-free).
+    """
+    return bool(flag_value) and (is_loopback(listen_address) or network_mode.lower() == 'personal_cloud')
+
+
 def do_nothing():
     pass