fix #417: world ambience kept playing at character select after the in-world logoff

The character-session reset manifest had no audio step: retail's logoff
destroys the world's sound sources with the world, but our OpenAL world
pool and ambient scheduler are process-lifetime — the continuous ambient
beds played on at character select and the scheduler kept RE-FIRING
deadlines against the stale listener (Suspend/StopAll had zero callers;
WorldGenerationQuiescence only cycles around teleport-style generation
replaces).

New WorldAudioSessionGate: the reset manifest's 'world audio' step stops
all sixteen world-pool voices (SuspendWorldAudio) and drops every ambient
deadline (StopAll); the pool reopens at the entered-world edge through the
new default-null LiveSessionEnteredWorldBindings.ResumeWorldAudio binding,
invoked first in ApplyEnteredWorld. The ambient soundscape needs no
explicit resume — the next objcell observation rebuilds it exactly as a
cell change always did. Covers logout, reconnect, and full stop uniformly.
UI-pool sounds (interface bank, portal cues) untouched by design.

App tests 5568/3 skips, Runtime 1756/0.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/AcDream.App.Tests/Net/LiveSessionResetPlanTests.cs

@@ -210,6 +210,7 @@ public sealed class LiveSessionResetPlanTests
             MouseCapture = Stage("mouse capture"),
             PlayerPresentation = Stage("player presentation"),
             TeleportPresentation = Stage("teleport presentation"),
+            WorldAudio = Stage("world audio"),
             SessionDialogs = Stage("session dialogs"),
             SettingsCharacterContext = Stage("settings character context"),
             EquippedChildren = Stage("equipped children"),
@@ -295,6 +296,7 @@ public sealed class LiveSessionResetPlanTests
         "mouse capture",
         "player presentation",
         "teleport presentation",
+        "world audio",
         "session dialogs",
         "settings character context",
         "equipped children",

tests/AcDream.App.Tests/Runtime/CurrentGameRuntimeAdapterTests.cs

@@ -1019,6 +1019,7 @@ public sealed class CurrentGameRuntimeAdapterTests
             MouseCapture = noop,
             PlayerPresentation = noop,
             TeleportPresentation = noop,
+            WorldAudio = noop,
             SessionDialogs = noop,
             SettingsCharacterContext = noop,
             EquippedChildren = noop,