v5.0.0: version bump, audit fixes, documentation overhaul

Version bumped to 5.0.0 across include/zupt.h, all packaging recipes, man
page, and docs.

Audit fixes (pre-5.0.0 review):
- src/zupt_format.c: overflow-safe bound in the solid-mode `test` path
  (off+sz could wrap and drive an OOB read in zupt_xxh64 on a crafted archive;
  the extract path was already hardened, the test path was not).
- gui: run_async now marshals the completion callback onto the GUI thread with
  QueuedConnection (a bare functor connected DirectConnection and touched
  widgets off the worker thread); Extract auto-detect note survives the log
  clear via a new `info` param.
- .github/workflows/ci.yml: trigger on `master` (was main/develop, so CI never
  ran); `make dist` tarball is vaptvupt-*.tar.gz not zupt-*; the ASAN PQ
  round-trip uses native --pq (was --pq-sdk, which fails on the source-only
  build and blocked the release job).

Documentation:
- New AUDIT.md (methodology, FIPS 203 conformance validation, findings, repro).
- CHANGELOG 5.0.0 entry covers the FIPS 203 conformance fix + BREAKING note and
  the GUI/CLI/security/packaging work.
- README "What's new in 5.0.0", download tables (incl. Windows/macOS/BSD +
  portable GUI), version-history row.
- SECURITY.md + THREAT_MODEL.md: ML-KEM-768 documented as FIPS 203, validated
  byte-for-byte against OpenSSL 3.5.
- Accuracy fixes: man page (--kdf default is PBKDF2 on source-only; codec
  2.60.4), rpm %description, debian control/copyright, homebrew header
  (no vendored library on source-only builds).

make check 16/16 (FIPS 203 conformance 3/3, all distro-safe checks).

doc/vaptvupt.1

@@ -1,7 +1,7 @@
 .\" Manpage for vaptvupt (formerly zupt; INPI Brasil trademark rename in v3.0.0)
 .\" SPDX-License-Identifier: AGPL-3.0-or-later
 .\" Copyright (c) 2025-2026 Cristian Cezar Moisés
-.TH VAPTVUPT 1 "July 2026" "vaptvupt 4.2.1" "User Commands"
+.TH VAPTVUPT 1 "July 2026" "vaptvupt 5.0.0" "User Commands"
 
 .SH NAME
 vaptvupt \- post-quantum backup compression utility (formerly zupt)
@@ -72,7 +72,7 @@ every byte of the archive — header, footer, per-block metadata, comments — i
 .PP
 The compression layer is the
 .B VaptVupt LZ + ANS
-codec (version 2.53.3), which prioritises decode speed and ratio over
+codec (version 2.60.4), which prioritises decode speed and ratio over
 encode speed. Aggregate decode throughput on this build is 1.27\(mu
 zstd\-3; encode throughput is 0.2\(mu\(en0.5\(mu zstd\-3 depending on
 content. See
@@ -239,9 +239,10 @@ Read password from file descriptor N.
 
 .TP
 .B --kdf \fIalgo\fR
-Choose key-derivation function for password mode:
-.BR argon2id " (default since v2.4.1; memory-hard) or "
-.BR pbkdf2 " (SHA-256, 600 000 iter; needed for compatibility with v2.4.0 and earlier readers)."
+Choose key-derivation function for password mode. In the default source-only
+build the only KDF is
+.BR pbkdf2 " (SHA-256, 600 000 iter), which is the default;"
+.BR argon2id " (memory-hard) is available only in a " WITH_SDK=1 " build."
 
 .TP
 .B --keyfile \fIpath\fR