server: serialize card access, fix poll-interval 0, add --timing

--poll-interval 0 now really disables background STATUS polling (it was
clamped to 1s, and the equip branch force-enabled it anyway). Request
handlers and the poll thread now share _CARD_LOCK so a poll can never
interleave a FETCH/TERMINAL RESPONSE pair — the baseline log showed
AUTO-STATUS chains and duplicate FETCHes inside the equip TP chain.

--timing adds elapsed timestamps, per-reset logging (RESET #n) and
phase durations for startup (init_reader, card_init, pysim_app,
terminal_profile_drain) and equip (onecmd, terminal profile).

AGENTS.md documents the proactive-TR invariant: never fetch without
answering, never fetch twice, one APDU conversation at a time.

tests/test_poll.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+"""Tests for the background STATUS polling interval semantics."""
+
+import sys
+import unittest
+from pathlib import Path
+from unittest import mock
+
+PROJECTS = Path(__file__).resolve().parents[2]
+PY_SIM = PROJECTS / 'pysim'
+if str(PY_SIM) not in sys.path:
+    sys.path.insert(0, str(PY_SIM))
+
+import pysim_otaman_server.server as S
+
+
+class TestPollInterval(unittest.TestCase):
+    def setUp(self):
+        self.saved = (S._POLL_ENABLED, S._POLL_INTERVAL, S._POLL_TIMER)
+
+    def tearDown(self):
+        S._poll_disable()
+        S._POLL_ENABLED, S._POLL_INTERVAL, S._POLL_TIMER = self.saved
+
+    def test_zero_interval_disables_polling(self):
+        S._set_poll_interval(0)
+        self.assertEqual(S._POLL_INTERVAL, 0)
+        with mock.patch.object(S.threading, 'Timer') as timer:
+            S._poll_enable()
+            timer.assert_not_called()
+        self.assertFalse(S._POLL_ENABLED)
+        self.assertIsNone(S._POLL_TIMER)
+
+    def test_negative_interval_clamped_to_zero(self):
+        S._set_poll_interval(-5)
+        self.assertEqual(S._POLL_INTERVAL, 0)
+
+    def test_positive_interval_starts_timer(self):
+        S._set_poll_interval(30)
+        with mock.patch.object(S.threading, 'Timer') as timer:
+            S._poll_enable()
+            self.assertTrue(S._POLL_ENABLED)
+            timer.assert_called_once_with(30, S._do_status_poll)
+
+    def test_reset_timer_skipped_when_disabled(self):
+        S._set_poll_interval(0)
+        S._POLL_ENABLED = True
+        with mock.patch.object(S.threading, 'Timer') as timer:
+            S._reset_poll_timer()
+            timer.assert_not_called()
+        self.assertIsNone(S._POLL_TIMER)
+
+
+if __name__ == '__main__':
+    unittest.main()