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/archipelago/src/api/rpc/openwrt.rs

@@ -135,7 +135,7 @@ impl RpcHandler {
                 // not /usr/bin/tollgate-module-basic-go — that's only the opkg/apk
                 // *package* name, never an on-disk filename.
                 let tollgate_installed = router
-                    .run("/usr/bin/opkg list-installed 2>/dev/null | grep -q '^tollgate-module-basic-go ' || \
+                    .run("opkg list-installed 2>/dev/null | grep -q '^tollgate-module-basic-go ' || \
                           test -f /usr/bin/tollgate-wrt 2>/dev/null")
                     .map(|(_, code)| code == 0)
                     .unwrap_or(false);