refactor(util): move is_ipv4_literal out of pipelock.py into util.py

The classifier is a pure dotted-quad regex check — nothing
pipelock-specific about it. Pipelock now imports it from util.
test_pipelock_classify.py retargets at the new location.

Two manifest-accessor functions in pipelock.py
(pipelock_bottle_allowlist, pipelock_bottle_ssh_hostnames) look
generic but are 1-line wrappers used only internally; they stay
for now.

tests/test_pipelock_classify.py

@@ -1,10 +1,10 @@
 """Unit: is_ipv4_literal — the classifier that decides whether
-bottle.ssh[].Hostname goes into ssrf.ip_allowlist (IPv4 literal) or
-trusted_domains (hostname)."""
+bottle.ssh[].Hostname goes into pipelock's ssrf.ip_allowlist (IPv4
+literal) or trusted_domains (hostname)."""
 
 import unittest
 
-from claude_bottle.pipelock import is_ipv4_literal
+from claude_bottle.util import is_ipv4_literal
 
 
 class TestIPv4Classify(unittest.TestCase):