Add macOS support, fix bloom filter routing and MMP intervals

macOS platform:
- Platform-native TUN interface management with shutdown pipe
- Raw Ethernet transport with macOS socket backend (socket_macos.rs)
- EthernetTransport and TransportHandle::Ethernet ungated from Linux-only
- macOS .pkg packaging (build-pkg.sh, launchd plist, uninstall script)
- CI: macOS build and unit test jobs; x86_64 cross-compiled from
  macos-latest via rustup target add x86_64-apple-darwin

Gateway feature flag:
- New opt-in `gateway` Cargo feature activates optional `rustables` dep
- `pub mod gateway` and `Config.gateway` gated behind the feature so
  macOS builds never pull in Linux-only nftables bindings
- `fips-gateway` bin has `required-features = ["gateway"]`
- All Linux/OpenWrt/AUR packaging passes `--features gateway`

CI / packaging:
- package-linux, package-macos, package-openwrt now trigger on push to
  master/maint/next and on pull requests; release uploads remain tag-gated
- Bloom filter routing fix: fall through to tree routing when no candidate
  is strictly closer
- MMP intervals: raise MIN to 1s / MAX to 5s with 5-sample cold-start phase

packaging/Makefile

@@ -8,6 +8,7 @@
 #   make tarball    Build a systemd install tarball
 #   make ipk        Build an OpenWrt .ipk package
 #   make aur        Build fips-git AUR package and validate with namcap
+#   make pkg        Build a macOS .pkg installer
 #   make all        Build deb and tarball (default)
 #   make clean      Remove deploy/ directory
 
@@ -15,7 +16,7 @@ SHELL := /bin/bash
 PACKAGING_DIR := $(dir $(abspath $(lastword $(MAKEFILE_LIST))))
 PROJECT_ROOT  := $(abspath $(PACKAGING_DIR)/..)
 
-.PHONY: all deb tarball ipk aur clean
+.PHONY: all deb tarball ipk aur pkg clean
 
 all: deb tarball
 
@@ -31,5 +32,8 @@ ipk:
 aur:
 	@bash $(PACKAGING_DIR)/aur/build-aur.sh
 
+pkg:
+	@bash $(PACKAGING_DIR)/macos/build-pkg.sh
+
 clean:
 	rm -rf $(PROJECT_ROOT)/deploy