feat(transport): fleet-wide bundle-unlock throttle window (register row 52)

The per-IP unlock throttle's counters were a process-local ConcurrentDictionary
on each central node, so the effective fleet cap was N x
MaxUnlockAttemptsPerIpPerHour per client (failing over to the other node handed
the client a fresh budget) and a node restart cleared the window outright.

The window now lives in the central MS SQL BundleUnlockAttempt table — the HA
store both central nodes already share, so no new infrastructure, no new port,
no consensus protocol:

- Commons: BundleUnlockAttempt entity + IBundleUnlockAttemptRepository.
- ConfigurationDatabase: entity config (one index,
  IX_BundleUnlockAttempt_Client_Attempted, serving both the windowed count and
  the prune), repository (AsNoTracking count, ExecuteDeleteAsync prune),
  DbSet, DI registration, migration AddBundleUnlockAttemptTable + the
  hand-written idempotent production script under docs/plans/sql/.
- Transport: IBundleUnlockAttemptWindow seam + SqlBundleUnlockAttemptWindow
  (singleton; resolves the scoped repository from its own scope per call, like
  the central purge singletons). BundleUnlockRateLimiter keeps the policy and
  gains TryRegisterAttemptAsync; BundleImporter.LoadAsync calls it.

Behaviour preserved from row 44: locked bundles spend no hourly budget (the
lockout check still runs first), throttle denials burn no per-bundle strike and
are NOT recorded so they cannot roll the window forward, unattributable clients
share the stricter <unattributed> bucket, and the budget counts attempts rather
than failures. Config keys and their semantics are unchanged, so the rig's 500
override stays valid.

Three deliberate trades, documented in both Transport docs:
- FAILS OPEN. A store error logs a Warning naming the client and cap, and
  permits the attempt. This is a best-effort rate cap over an already
  authenticated, Administrator-gated surface — the availability of legitimate
  imports outranks the cap, and a DB blip must not make the import wizard
  unusable. Falling back to the process-local window was considered and
  rejected: it would still block a legitimate operator's 11th import.
- Approximate. Count-then-insert is not atomic across nodes, so simultaneous
  attempts can overshoot by the number in flight — bounded, self-correcting
  within the window, and not worth provider-specific raw SQL.
- Pruned opportunistically on the unlock path (CAS-claimed at most every 15
  min per process, bounded to 1000 rows, retaining 2x the window, best-effort
  try/catch) rather than by a new background service — Transport owns no
  central scheduler. Same shape as DeploymentService's terminal-record sweep.

Tests: Transport.IntegrationTests 116 passed (+10 — two limiter instances over
one store enforcing a single combined window, restart durability, denials
burning no budget, sliding release, bucket isolation, store-failure fail-open,
caller-cancellation not swallowed, no-shared-window fallback, prune and its
negative control); ConfigurationDatabase 395 passed (+5).

src/ZB.MOM.WW.ScadaBridge.Transport/Import/BundleImporter.cs

@@ -293,11 +293,18 @@ public sealed class BundleImporter : IBundleImporter
             //     operator is legitimately importing.
             // Registered on every unlock attempt (successful ones included) because the
             // documented budget counts attempts, not failures.
+            //
+            // Register row 52: the async overload consults the FLEET-WIDE window (central
+            // MS SQL) so the cap is not multiplied by the number of central nodes and does
+            // not reset on a node restart. It fails open on a store error — see
+            // BundleUnlockRateLimiter's remarks.
             var throttleKey = string.IsNullOrWhiteSpace(clientKey)
                 ? UnattributedClientKey
                 : clientKey;
             var perIpCap = _options.Value.MaxUnlockAttemptsPerIpPerHour;
-            if (!_unlockRateLimiter.TryRegisterAttempt(throttleKey, perIpCap))
+            if (!await _unlockRateLimiter
+                    .TryRegisterAttemptAsync(throttleKey, perIpCap, ct)
+                    .ConfigureAwait(false))
             {
                 _logger?.LogWarning(
                     "Bundle unlock throttled: client {ClientKey} exceeded {Cap} attempts in the trailing hour.",