fix(ipc): reset the state subscription's reconnect wait after a good connection (#740)

StateSubscription._run reset its backoff only when _follow() returned
normally, which happens only on stop(). Every real disconnect raises
ControlError, so the wait kept doubling across connections: after
successive display restarts the web resubscribed 1, 2, 4, 8, 16 and then
30 s later for good, answering from one-shot state.get connections in the
meantime. The docs promise "1 s up to 30 s" per outage.

The wait now goes back to the minimum once a connection got as far as
storing a snapshot, whatever ended it. A display without the stream
(unknown_command) is still retried at the slow interval.

The frozen-timestamp bug found in the same review is fixed by #737.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -515,6 +515,16 @@ policies are unchanged.
   `DisplayManager.cleanup()` (reached from SIGTERM through `run()`'s
   `finally`) unregisters it with the frame recorder. New
   `frame_timing.uninstall_gc_monitor()`.
+- The web interface's state subscription (`StateSubscription`,
+  `src/ipc/client.py`) resubscribes about 1 s after a display restart, every
+  time. Its reconnect wait went back to the minimum only when the
+  subscription was stopped. A disconnect after a working connection kept
+  doubling the wait, so successive display restarts were followed by waits
+  of 1, 2, 4, 8, 16 and then 30 s for good.
+  During each wait the web answered from one-shot `state.get` connections
+  instead of its copy. The wait now resets once a connection has stored a
+  snapshot. A display that does not offer the stream is still retried
+  slowly.
 - A plugin reload after a store update (`plugin.reload`, #720) no longer
   freezes the panel during Vegas. On ledpi a football reload froze it for
   3.0 s (`Render stall over: no frame for 3043ms`). The reload ran on the