GUI rework for source-only builds + CLI security fixes + packaging + cross-platform scaffolding

Fixes the "GUI functions don't work on GNU Guix" report and a batch of
adversarial-audit findings across the CLI, decoder, crypto and packaging.

GUI (gui/src/zupt_gui.py)
- Root cause of the broken GUI: every encryption path defaulted to the
  libzuptsdk "SDK v2" modes, which are absent from the source-only build and
  exit 1. Reworked Keys/Compress/Extract around the native modes with a
  build-aware PQ-mode selector: Hybrid (--pq, default), Full PQ (--pq-only),
  and SDK v2 only when the binary reports WITH_SDK support. Capability is
  detected from `version` ("Build:"/"KDF:" lines) with a `help` fallback.
- Extract/Verify gain a PQ private-key input with auto-detect (reads the
  archive via `info` to pick --pq vs --pq-only). Verify could not verify any
  PQ archive before (password field only).
- run_async now holds a LIST of in-flight (thread, worker) refs; DiskTab's two
  buttons previously shared one slot, so a second op GC'd the first QThread
  mid-run. About tab corrected (codec 2.60.4, PBKDF2 default, --pq-only, URL).

CLI (src/zupt_main.c)
- compress -p <archive> <files> swallowed the archive name as the password and
  truncated the first input file (silent data loss, exit 0). Added a
  data-loss guard: refuse to overwrite an existing non-.zupt file as the output
  archive unless -y/--force; plus a self-overwrite guard.
- compress <archive> <src> -p <pw> wrote an UNENCRYPTED archive (exit 0)
  because options after the first positional were treated as files. Now errors
  on a misplaced option (with a `--` escape for real dashed filenames).
- Removed duplicated dead --pq-box/--pq-sdk branches. version/banner/usage now
  state the build's real KDF (PBKDF2 on source-only) and repo URL; examples
  lead with native --pq / --pq-only.

Security (audit findings)
- vv_decoder.c: the two AVX2 fast-path token decoders read a 2-/3-byte match
  offset after only checking 1 byte remained -> heap over-read on a crafted
  archive. Added the `ip + off_bytes > ip_end` guard the tail path already had.
- zupt_crypto.c: wipe ML-KEM/X25519 secret-key buffers when hybrid decrypt
  init fails on key read (matches the pq-only path).
- zupt_format.c: bound attacker-controlled encryption_header_off before the
  (off_t)+7 arithmetic in the info enc_type reader (avoid signed-overflow UB).

Packaging (would fail source-only)
- debian/rules (staged into debian/zupt, installed vendored .so), aur/PKGBUILD,
  nix/flake.nix, homebrew (vendored .so + nonexistent AUDIT.md, stale /zupt
  URLs) now build source-only. opensuse spec %files ships the shell completions
  make install writes (rpmbuild no longer fails on unpackaged files);
  _service + debian/control point at the vaptvupt repo; KDF claim corrected.

Cross-platform GUI packaging (new)
- packaging/portable/: OS-agnostic GUI package (zupt_gui.py + .bat/.command/.sh
  launchers + README) that runs on Windows/macOS/Linux/BSD with Python+PySide6.
- .github/workflows/cross-platform.yml: builds real native binaries on
  windows-latest + macos-latest runners (CLI, PyInstaller GUI, Inno Setup
  installer, .dmg) and the portable zip, attaching them to the release on tag.
- packaging/windows/vaptvupt-gui.iss: Inno Setup installer script.

Validation: make check 16/16 (all distro-safe checks), GUI imports + command
contracts verified against the fixed CLI. test_help_consistency updated to
assert the truthful (build-aware) default KDF.

packaging/debian/control

@@ -8,9 +8,9 @@ Build-Depends:
  libc6-dev,
  python3 (>= 3.8)
 Standards-Version: 4.6.2
-Homepage: https://git.securityops.co/cristiancmoises/zupt
-Vcs-Browser: https://git.securityops.co/cristiancmoises/zupt
-Vcs-Git: https://git.securityops.co/cristiancmoises/zupt.git
+Homepage: https://git.securityops.co/cristiancmoises/vaptvupt
+Vcs-Browser: https://git.securityops.co/cristiancmoises/vaptvupt
+Vcs-Git: https://git.securityops.co/cristiancmoises/vaptvupt.git
 Rules-Requires-Root: no
 
 Package: vaptvupt
@@ -24,7 +24,7 @@ Description: Post-quantum backup compression utility (formerly Zupt)
  a pure-C11 backup compression utility featuring:
   * Post-quantum hybrid encryption (ML-KEM-768 + X25519, FIPS 203)
   * AES-256-CTR + HMAC-SHA256 authenticated encryption (Encrypt-then-MAC)
-  * Argon2id password-based key derivation (default since 2.4.1)
+  * PBKDF2-SHA256 password key derivation (Argon2id in WITH_SDK=1 builds)
   * Multi-threaded compression with the VaptVupt LZ + ANS codec 2.48.5
   * Full-disk backup and restore with sparse-region detection
   * End-to-end byte-level tamper detection on encrypted archives

packaging/debian/rules

@@ -14,20 +14,18 @@ export DEB_LDFLAGS_MAINT_APPEND = -Wl,--as-needed
 	dh $@
 
 override_dh_auto_build:
-	$(MAKE) -j$$(nproc)
+	# Source-only build: no vendored libraries, native crypto only.
+	$(MAKE) WITH_SDK=0 -j$$(nproc)
 
 override_dh_auto_test:
-	# Project's own regression suite covers F-06..F-12.
-	$(MAKE) test
+	# Distro-safe regression subset (F-06..F-12, dedup-nonce, NIST/RFC vectors).
+	$(MAKE) WITH_SDK=0 check
 
 override_dh_auto_install:
-	$(MAKE) DESTDIR=$(CURDIR)/debian/zupt PREFIX=/usr install
-	# Vendored libzuptsdk goes alongside the binary at a relative rpath.
-	install -d $(CURDIR)/debian/zupt/usr/lib/zupt
-	install -m 0755 vendor/zuptsdk/libzuptsdk.so.2.0.0 \
-		$(CURDIR)/debian/zupt/usr/lib/zupt/libzuptsdk.so.2.0.0
-	ln -sf libzuptsdk.so.2.0.0 $(CURDIR)/debian/zupt/usr/lib/zupt/libzuptsdk.so.2
-	ln -sf libzuptsdk.so.2.0.0 $(CURDIR)/debian/zupt/usr/lib/zupt/libzuptsdk.so
+	# Binary package is `vaptvupt` -> stage into debian/vaptvupt (dh derives the
+	# staging dir from the Package: name in debian/control). Source-only: nothing
+	# to install beyond `make install` (no .so).
+	$(MAKE) DESTDIR=$(CURDIR)/debian/vaptvupt PREFIX=/usr WITH_SDK=0 install
 
 override_dh_auto_clean:
 	$(MAKE) clean