perf #418: publish landblocks under the meter, not one per streaming tick

Phase-1 measurement (new [publish-timing]/[stream-tick] probe surfaces,
ACDREAM_PROBE_REVEAL_TIMING=1) refuted the ~31 ms-per-admission
hypothesis: the hold runs at ~64 fps with the streaming tick at ~32 Hz,
the whole 625-block window costs only ~500 ms of publication CPU (far
blocks ~0.17 ms, near 2-43 ms), and steady state showed ZERO meter
yields with ~0.22 ms of the 2 ms budget used - yet exactly one block
published per tick against a ~400-deep completion queue.

The real limiter: Runtime's collision-generation activation is a
deliberate two-poll transaction (the first
TryAcquireCollisionPrefixMutationPermission poll parks residents and
refuses by design), and LandblockPresentationPipeline.Advance's metered
arm returned Completed=false on ANY nonterminal commit, which
DrainAndApply treats as end-of-frame. One landblock per 32 Hz tick =
the flat 32/s, with the authored budget ~90% idle.

Fix: the metered arm now uses the same Runtime-owned gate the unmetered
arm and the synchronous CompletePublication API always used
(CanContinueMutationSynchronously). The second poll runs in the same
frame under the same meter, so the unchanged 2 ms elapsed-time ceiling
is now genuinely the authoritative per-frame bound; with any real debt
(live residents parked mid-game, pending withdrawals, dispatch backlog)
publication defers to the next frame exactly as before. No budget
values change, no reveal-gate/readiness change, and the streamed result
is byte-identical - only the frame scheduling of identical operations.

Measured A/B (this binary, two runs): totalMs 12689 / 12734 vs baseline
26728/27395/27503; loaded slope 32/s -> bursts of 100-360/s, 625/625 in
~6-7 s vs ~23 s. The remaining ~12.7 s floor is fully attributed in
docs/ISSUES.md: ~8 s of real budgeted readiness work plus retail's
authored tunnel exit (TunnelContinue 2-5 s + two 1 s fades, golden
constants), so the <12 s acceptance needs a lead decision on the
hold-time budget, not another hidden limiter.

New regression pin:
MeteredLoaded_NonterminalCommitWithoutDebt_CompletesInOneMeteredAdvance.
Gates: Release build 0 errors; App tests 5576/3 skips/0 failed;
Runtime tests 1756/0.

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

src/AcDream.App/Streaming/StreamingController.cs

@@ -778,6 +778,13 @@ public sealed class StreamingController
             ObserveWorkLifetime(snapshot);
             _lastWorkMeter = snapshot;
             _activeWorkMeter = null;
+            if (PublicationTimingProbe.Enabled)
+            {
+                PublicationTimingProbe.ObserveStreamingTick(
+                    snapshot,
+                    _completionSource.BacklogCount,
+                    _completionQueue.Count);
+            }
         }
     }