v4.0.0: codec 2.60.4 security release, --pq-box sealed-box mode, F-16 fix

Major release. Highlights:

- Codec: vendored VaptVupt codec moves to canonical 2.60.4 security
  release. Fixes a high-severity OOB heap write in the AVX2 decode fast
  path (reachable on a valid stream sized to exactly content_size, both
  tail variants). Brings CBMC-formally-verified BCJ filters with
  automatic ELF/PE/Mach-O detection. Compressed output stays
  byte-identical (ratio gate Δ 0.00%); wire format unchanged at v1.6.
- New --pq-box sealed-box recipient mode (vendored libpqvaptvupt 0.6.0):
  ML-KEM-768 + X25519 combined via HKDF-SHA256 with domain separation,
  AES-256-CTR + HMAC-SHA256 EtM. Legacy --pq and --pq-sdk stay readable.
- F-16: discloses and fixes a pre-existing data-loss defect in the
  <= 3.8.0 in-tree BCJ encoder. Full back-compat matrix decodes
  byte-exact under 4.0.0; every readable pre-4.0 archive remains readable.

Repository hygiene:
- Sync full 4.0.0 source tree (codec, crypto, SDK, GUI, packaging, tests).
- Remove internal scratch files (PROMPT.md, FORMAL_AUDIT_PROMPT.md)
  and superseded version-specific docs (INTEGRATION_PROTOCOL_2.60.4.md,
  docs/FINDINGS-2.x.md) and a stray test binary.
- Refresh README download/install section to real 4.0.0 release assets;
  bump version badge to 4.0.0.
- Add .gitignore for build outputs (keeps vendored prebuilt libraries).

packaging/debian/control

@@ -0,0 +1,41 @@
+Source: vaptvupt
+Section: utils
+Priority: optional
+Maintainer: Cristian Cezar Moisés <sac@securityops.co>
+Build-Depends:
+ debhelper-compat (= 13),
+ gcc,
+ 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
+Rules-Requires-Root: no
+
+Package: vaptvupt
+Architecture: any
+Provides: zupt (= ${binary:Version})
+Replaces: zupt
+Conflicts: zupt
+Depends: ${shlibs:Depends}, ${misc:Depends}
+Description: Post-quantum backup compression utility (formerly Zupt)
+ VaptVupt (renamed from Zupt in v3.0.0 due to INPI Brasil trademark) is
+ 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)
+  * 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
+    (0 silent-accept positions in the v1.6 exhaustive byte sweep)
+  * Constant-time cryptographic primitives verified with Jasmin
+  * NIST/RFC test vectors for SHA-256, SHA-3, ML-KEM-768, AES-256-CTR,
+    HMAC-SHA256, X25519, PBKDF2, Argon2id
+ .
+ The archive extension stays .zupt for format continuity (header magic
+ unchanged). The binary `zupt` is preserved as a symlink to `vaptvupt`.
+ .
+ The archive format includes an integrity trailer that authenticates the
+ header and footer, per-block HMAC with bound frame-preface AAD, and
+ optional encrypted comments.