fix(cred_proxy): close git-push bypass + route through pipelock (PRD 0010)

Three coupled fixes that close a documented bypass of git-gate's
gitleaks pre-receive hook:

1. cred-proxy refuses git smart-HTTP push at runtime. Any path
   ending in /git-receive-pack or /info/refs?service=git-receive-pack
   returns 403 with a pointer at the bottle.git SSH path. Fetch
   (upload-pack) is still allowed — the bypass we're closing is
   push, where gitleaks is the load-bearing scanner. Hard guarantee.

2. The provisioner suppresses the cred-proxy `~/.gitconfig` insteadOf
   rewrite for any host already declared in bottle.git. git-gate is
   the canonical git path there; we don't write a competing rule
   that would let `git clone https://<host>/...` succeed in ways
   that confuse on push. Defense in depth — (1) is the hard guarantee.

3. cred-proxy routes its outbound HTTPS through pipelock. The
   sidecar's environ now sets HTTPS_PROXY=<pipelock-url>, and the
   image's entrypoint runs `update-ca-certificates` over the
   per-bottle pipelock CA (docker cp'd into
   /usr/local/share/ca-certificates/pipelock.crt before start) so
   the proxy's HTTPS client trusts pipelock's bumped certs.

   Consequence: pipelock's allowlist + body scanner now sit in the
   cred-proxy egress path the same way they sit in front of direct
   agent traffic. The cred-proxy upstream hosts (api.github.com,
   github.com, gitea hosts, registry.npmjs.org) come OFF
   pipelock's passthrough_domains. Only api.anthropic.com remains
   on passthrough (LLM body content legitimately trips DLP).

PRD 0010 updated to reflect all three. Tests adjusted: the
"cred-proxy hosts go on passthrough" assertion in
test_pipelock_allowlist flips to "they don't", a new
TestIsGitPushRequest exercises the smart-HTTP refusal predicate,
and the gitconfig renderer tests cover the per-host suppression
matrix.

tests/unit/test_pipelock_allowlist.py

@@ -92,9 +92,13 @@ class TestTlsPassthrough(unittest.TestCase):
         passthrough = pipelock_effective_tls_passthrough(_bottle({}))
         self.assertEqual(["api.anthropic.com"], passthrough)
 
-    def test_token_hosts_added_to_passthrough(self):
-        # cred-proxy validates upstream certs with the real CA bundle;
-        # pipelock must not MITM these or the handshake fails.
+    def test_token_hosts_NOT_added_to_passthrough(self):
+        # cred-proxy now trusts pipelock's per-bottle CA (loaded into
+        # its container's trust store via docker cp + update-ca-
+        # certificates at start time), so pipelock can MITM the
+        # cred-proxy -> upstream leg and body-scan it. Auto-adding
+        # cred-proxy hosts to passthrough would silently disable that
+        # second scanner for github / gitea / npm.
         passthrough = pipelock_effective_tls_passthrough(_bottle({
             "tokens": [
                 {"Kind": "github", "TokenRef": "G"},
@@ -103,10 +107,7 @@ class TestTlsPassthrough(unittest.TestCase):
                  "Url": "https://gitea.dideric.is"},
             ],
         }))
-        for host in ("api.anthropic.com", "api.github.com", "github.com",
-                     "registry.npmjs.org", "gitea.dideric.is"):
-            self.assertIn(host, passthrough)
-        self.assertEqual(passthrough, sorted(passthrough), "sorted")
+        self.assertEqual(["api.anthropic.com"], passthrough)
 
 
 if __name__ == "__main__":