Style command + GET RESPONSE pairs in the APDU list; bump to 1.15.0

- Pair members (a command ending '61 XX' and its GET RESPONSE, via the
  server-side response_for link) get a subtle slate row tint
  (--pair-row, themed: rgba(148,163,184,.12) dark / rgba(100,116,139,.15)
  light); hover/selected still take precedence.
- Paired GET RESPONSE rows are prefixed with '↳' marking them as a
  continuation of the previous command; orphaned GRs stay plain.
- GET RESPONSE label uses cat-gr class: muted color, weight 600 like
  other command names.
- Map view untouched (it skips GRs); detail view already shows
  "Response for".

Version 1.15.0, SW cache simtrace-analyser-v20.

tests/test_pcap_import.py

@@ -197,7 +197,7 @@ class TestImportEndpoint(unittest.TestCase):
 class TestVersion(unittest.TestCase):
     def test_package_version(self):
         from simtrace2_pysniff import __version__
-        self.assertEqual(__version__, '1.14.0')
+        self.assertEqual(__version__, '1.15.0')
 
     def test_status_includes_version(self):
         import os