feat: F5.6c measured and accepted on test-filius; tickets up to 5 s ahead of F's clock

test-filius refused every ticket as from the future: its clock was 886 ms
behind the dashboard's machine, with NTP still 8 ms (one ticket in 125, as a
ticket carries whole seconds). F now takes a ticket signed up to 5 s ahead
(TICKET_AHEAD_SECONDS); itsdangerous refuses one second, and the oracle
keeps that on record.

tools/live measures and accepts on a live F, with fresh projects each run:
m3 (200 rooms of the largest example with pings: probe p95 37 ms), m4 (63 KB
document; dragging makes an update per pointer move, 59/s), m5 (an hour
through the proxy), acceptance (two browsers, 14 checks, passed three times)
and clock (F's clock against ours).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/server/test/tickets.python.json

@@ -88,6 +88,18 @@
       "now": 1789999999,
       "error": "expired"
     },
+    {
+      "name": "fiveSecondsAhead",
+      "ticket": ".eJwVi0kKwzAMAL9S1GsF8Rq7t_YnsiQXQwih66H071VuwzDzhRecYWqlp-4VHQXGKEmx9Dqh8yGmPJdKjeEEq6XUnDcUw4vQ4arjsQ1dTLGpYwg5894utN5MiBpvBrk78RwaRkoVoxbBynNDcs20RE0979t7sfhzH0-F3x-ZYioB.arE7gA.xwmcG5wEqkYKe3DxNMUxtEnXaQo",
+      "now": 1789999995,
+      "error": "expired"
+    },
+    {
+      "name": "sixSecondsAhead",
+      "ticket": ".eJwVi0kKwzAMAL9S1GsF8Rq7t_YnsiQXQwih66H071VuwzDzhRecYWqlp-4VHQXGKEmx9Dqh8yGmPJdKjeEEq6XUnDcUw4vQ4arjsQ1dTLGpYwg5894utN5MiBpvBrk78RwaRkoVoxbBynNDcs20RE0979t7sfhzH0-F3x-ZYioB.arE7gA.xwmcG5wEqkYKe3DxNMUxtEnXaQo",
+      "now": 1789999994,
+      "error": "expired"
+    },
     {
       "name": "otherSecret",
       "ticket": ".eJwVi0kKwzAMAL9S1GsF8Rq7t_YnsiQXQwih66H071VuwzDzhRecYWqlp-4VHQXGKEmx9Dqh8yGmPJdKjeEEq6XUnDcUw4vQ4arjsQ1dTLGpYwg5894utN5MiBpvBrk78RwaRkoVoxbBynNDcs20RE0979t7sfhzH0-F3x-ZYioB.arE7gA.4wnVSAZOvBXnfPb_aCCd2137AEI",