fix(git-clone): accept HTTPS repo URLs on any host, not just GitHub

scanners/lib/git-clone.mjs accepted only github.com, so the README's
Forgejo example (and /security scan on any Forgejo, Codeberg or self-hosted
URL) failed validation; scan.md and plugin-audit.md also routed only
https://github.com/ to the clone path.

Chose generic HTTPS over adding one host to an allowlist because there is
no documented security reason for the host check. Read before choosing:
git log --follow (import + E12 only), the file's comments, CHANGELOG v2.4.0
("GitHub repo URL support", feature framing), security-hardening-guide §2
and §7 (the sandbox is the defence against filter/smudge drivers), and
review-2026-06-20, which lists "vsix-fetch (HTTPS host allowlist)" as a
protection but no host check for git-clone. What protects a clone is the
OS sandbox, GIT_SANDBOX_CONFIG and GIT_SANDBOX_ENV, for every host alike.

Measured: with GIT_SANDBOX_ENV, git reads 0 config lines outside a repo;
without it, osxkeychain comes from Xcode's system gitconfig. So no stored
credential is offered to an unknown host.

The shape stays strict: https only, no userinfo, host starts and ends
alphanumeric (no leading -), optional port, exactly owner/repo, no query
or fragment. SSH stays GitHub-only: ssh uses the user's own keys and
~/.ssh/config, which the git environment does not isolate.

Tests (red first): Forgejo and any-host accept 2 failing -> green; guards
for http, userinfo, leading -, extra path, query, ext:: and file:: and
non-GitHub SSH hold. The old "rejects non-GitHub URL" case still passes
(it has no owner/repo) and is renamed to say so. Regex timed linear
(< 1 ms at 200k chars). Live: a sandboxed clone of
https://git.fromaitochitta.com/open/llm-security.git exits 0 at 5208420,
cleaned up.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/lib/git-clone-sandbox.test.mjs

@@ -245,13 +245,41 @@ describe('git-clone validate', () => {
     assert.equal(result.status, 0);
   });
 
-  it('rejects non-GitHub URL', () => {
+  it('rejects an HTTPS URL without an owner/repo path', () => {
     const result = spawnSync('node', [GIT_CLONE, 'validate', 'https://evil.com/repo'], {
       encoding: 'utf8',
     });
     assert.equal(result.status, 1);
   });
 
+  // v8.1.0 S3: any HTTPS host. The host was never the boundary — the sandbox,
+  // the git config flags and the isolated environment are, for every host.
+  const validate = (url) => spawnSync('node', [GIT_CLONE, 'validate', url], { encoding: 'utf8' }).status;
+
+  it('accepts an HTTPS Forgejo URL', () => {
+    assert.equal(validate('https://git.fromaitochitta.com/open/llm-security.git'), 0);
+    assert.equal(validate('https://git.fromaitochitta.com/open/llm-security'), 0);
+  });
+
+  it('accepts an HTTPS URL on any host, with or without a port', () => {
+    assert.equal(validate('https://codeberg.org/org/repo'), 0);
+    assert.equal(validate('https://git.example.com:3000/org/repo.git'), 0);
+  });
+
+  it('keeps rejecting shapes that are not a plain HTTPS owner/repo URL', () => {
+    assert.equal(validate('http://git.example.com/org/repo'), 1, 'plain http');
+    assert.equal(validate('https://user:pass@git.example.com/org/repo'), 1, 'userinfo');
+    assert.equal(validate('https://-oProxyCommand=x/org/repo'), 1, 'host starting with -');
+    assert.equal(validate('https://git.example.com/org/repo/src/branch/main'), 1, 'extra path');
+    assert.equal(validate('https://git.example.com/org/repo?x=1'), 1, 'query');
+    assert.equal(validate('ext::sh -c touch% /tmp/x'), 1, 'ext transport');
+    assert.equal(validate('file:///etc/org/repo'), 1, 'file transport');
+  });
+
+  it('keeps SSH GitHub-only (ssh uses the user\'s own keys and config)', () => {
+    assert.equal(validate('git@git.example.com:org/repo.git'), 1);
+  });
+
   it('rejects URL with tree path', () => {
     const result = spawnSync('node', [GIT_CLONE, 'validate', 'https://github.com/org/repo/tree/main/dir'], {
       encoding: 'utf8',