Cross builds, packaging split, CI, fuzzing, supply-chain policy

build.sh builds the Rust targets with the Go-era names, refuses an OUT
that is /, $HOME or the tree, checks static linking and names the Go
targets Rust cannot build. packaging/package.sh builds and inspects
packages without signing or publishing; repo.sh reuses it. Seven fuzz
targets (one found a URL-parser panic, fixed here with a regression
test), cargo-deny policy, CI for lint, tests on Linux/macOS/Windows,
cross builds with qemu runs, supply chain and fuzzing. Compatibility
specification and security notes.

Co-Authored-By: Claude <noreply@anthropic.com>

fuzz/fuzz_targets/html.rs

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+//! The mirror's HTML and CSS rewriters never panic, and rewriting nothing
+//! returns the input byte for byte.
+#![no_main]
+use vault::net::html;
+
+libfuzzer_sys::fuzz_target!(|data: &[u8]| {
+    let _ = html::tokenize(data);
+    assert_eq!(html::rewrite_html(data, &mut |_| None, &mut |_| None), data);
+    assert_eq!(html::rewrite_css(data, false, &mut |_| None), data);
+    let _ = html::rewrite_html(data, &mut |_| None, &mut |u| Some(format!("x/{}", u.len())));
+    if let Ok(s) = std::str::from_utf8(data) {
+        let _ = vault::net::Url::parse(s).map(|u| u.join("../a?b#c"));
+    }
+});