sdk: integrate libvuptsdk (renamed libzuptsdk); decouple --pq-box

libvuptsdk (git.securityops.co/cristiancmoises/libvuptsdk) is the renamed
libzuptsdk: only the .so filename/SONAME changed (libzuptsdk.so.2 ->
libvuptsdk.so.2); the C API (zuptsdk_* symbols, zuptsdk.h) is unchanged.

- Rename vendor/zuptsdk -> vendor/vuptsdk with libvuptsdk's headers.
- Makefile WITH_SDK=1 now links -lvuptsdk (+ its transitive libcrypto/libargon2
  deps via SDK_DEPLIBS) instead of -lzuptsdk, and installs libvuptsdk.so.*.
- DECOUPLE --pq-box: it needs the SEPARATE libpqvaptvupt, which libvuptsdk does
  NOT provide, so gate it behind a new WITH_PQBOX=1 (was folded into WITH_SDK).
  zupt_crypto_pqbox.c now keys on ZUPT_WITH_PQBOX; WITH_SDK=1 alone builds and
  links cleanly with just libvuptsdk and enables --pq-sdk + Argon2id.
- Banner/help renamed libzuptsdk -> libvuptsdk; the machine-readable 'Build:'
  line lists --pq-box only under WITH_PQBOX. GUI _get_caps matches on 'vuptsdk'.

Validated on Guix: WITH_SDK=1 links libvuptsdk + libcrypto + libargon2, runs,
banner 'Build: full (libvuptsdk: Argon2id, --pq-sdk available)', keygen --sdk +
--pq-sdk encrypt/decrypt byte-exact roundtrip. Default source-only build
unchanged (make check 16/16).

gui/src/zupt_gui.py

@@ -194,7 +194,7 @@ ZUPT_VER_SHORT, ZUPT_VER_NUMBER, ZUPT_VER_FULL = _get_version()
 
 # ── Detect build capabilities from `version` (and `help` as fallback) ──
 #
-# The default build is SOURCE-ONLY: the libzuptsdk-backed modes (Argon2id
+# The default build is SOURCE-ONLY: the libvuptsdk-backed modes (Argon2id
 # KDF, --pq-sdk, --pq-box) are absent and fail with exit 1. Offering them in
 # the UI is the #1 reason "functions don't work". We detect what THIS binary
 # actually supports and build the encryption UI around it:
@@ -212,7 +212,7 @@ def _get_caps():
     for line in blob.splitlines():
         low = line.lower()
         if low.startswith("build:"):
-            sdk = ("full" in low) and ("libzuptsdk" in low)
+            sdk = ("full" in low) and ("vuptsdk" in low)
         elif low.startswith("kdf:"):
             default_kdf = "Argon2id" if "argon2id (default)" in low else "PBKDF2-SHA256"
         if "--pq-only" in line: