docs: renumber PRD 0081 -> 0083 across the reconcile chunk

Follows the base PR's renumber (0081 was already taken; main is on 0082). Update
every `PRD 0081` reference in the gateway-attach code, tests, and ADR 0006, plus
ADR 0006's link to the PRD file. No behaviour change.

Refs #516, #519.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/unit/test_orchestrator_gateway.py

@@ -90,7 +90,7 @@ class TestDockerGateway(unittest.TestCase):
         self.assertEqual([], [c for c in calls if c[:2] == ["docker", "run"]])
         self.assertEqual([], [c for c in calls if c[:2] == ["docker", "rm"]])
         # A healthy current gateway left untouched is not a cold boot — the
-        # bring-up flow skips the running-bottle reconcile (PRD 0081).
+        # bring-up flow skips the running-bottle reconcile (PRD 0083).
         self.assertFalse(cold_booted)
 
     def test_ensure_running_recreates_when_image_is_stale(self) -> None:
@@ -113,7 +113,7 @@ class TestDockerGateway(unittest.TestCase):
         self.assertEqual(1, len([c for c in calls if c[:2] == ["docker", "run"]]))
         self.assertTrue(any(c[:2] == ["docker", "rm"] for c in calls))
         # A recreated container minted/mounted its CA afresh — a cold boot that
-        # triggers the running-bottle reconcile (PRD 0081).
+        # triggers the running-bottle reconcile (PRD 0083).
         self.assertTrue(cold_booted)
 
     def test_ensure_running_starts_the_singleton_when_absent(self) -> None: