fix(openwrt): resolve opkg/apk via $PATH, not a hardcoded /usr/bin path

opkg_check() and every opkg/apk invocation hardcoded /usr/bin/opkg and
/usr/bin/apk. Official OpenWrt images don't all symlink /bin into
/usr/bin — the glinet_gl-mt3000 24.10.2 build keeps them as separate
real directories with opkg living in /bin — so the check silently
missed a perfectly normal install and TollGate provisioning failed
with "this router's firmware may not support package management".

Switched every call to resolve through the router's own $PATH
(command -v / bare opkg / apk) instead. Reproduced and fixed live
against archy-x250-pa3, 2026-09-05.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0176RpCxFNS9ZaSJjL72W9Z5

core/openwrt/src/tollgate/install.rs

@@ -35,7 +35,7 @@ pub fn install_tollgate(router: &Router) -> Result<()> {
 
     // Package not in any feed — download the .ipk directly.
     let arch = router
-        .run_ok("/usr/bin/opkg print-architecture | grep -v all | grep -v noarch | tail -1 | awk '{print $2}'")?;
+        .run_ok("opkg print-architecture | grep -v all | grep -v noarch | tail -1 | awk '{print $2}'")?;
     let arch = arch.trim();
 
     let url = ipk_url(arch).ok_or_else(|| {
@@ -88,7 +88,7 @@ pub fn install_tollgate_apk_native(router: &Router) -> Result<()> {
         ". /etc/openwrt_release 2>/dev/null \
          && a=\"${DISTRIB_ARCH:-${OPENWRT_ARCH:-}}\" \
          && [ -n \"$a\" ] && echo \"$a\" \
-         || /usr/bin/apk --print-arch 2>/dev/null \
+         || apk --print-arch 2>/dev/null \
          || uname -m",
     )?;
     // Normalise: uname -m returns bare "mipsel"/"mips"; map to 24kc variant