refactor(sf,site): both stores take ILocalDb instead of a connection string

Tasks 5 and 6 of the Phase 2 plan, committed together because their test
fallout is entangled — several fixtures construct both stores.

StoreAndForwardStorage and SiteStorageService now take ILocalDb. Connections
come from ILocalDb.CreateConnection(), which hands out an already-open,
pragma-configured connection carrying the zb_hlc_next() UDF the capture triggers
call; a raw connection would lack the UDF and every write to a replicated table
would fail closed. Deleted with the connection strings: S&F's
EnsureDatabaseDirectoryExists and its per-open busy_timeout pragma, and the site
service's BusyTimeoutFloorSeconds normalization — LocalDb owns all of it now.

DI: AddSiteRuntime's string overload is gone (nothing left to supply), so the
Host calls the no-arg form. ScadaBridge:Database:SiteDbPath and
StoreAndForwardOptions.SqliteDbPath survive only as the migrator's source
locations in Tasks 8/9.

Two things the plan did not anticipate, both worth reading:

1. FOUND A REAL LATENT DEFECT, from Phase 1, now fixed. The plan assumed
   directory creation simply moved to LocalDb along with file ownership. It did
   not: the LocalDb library never creates the parent directory, and
   SqliteLocalDb opens the file eagerly in its constructor — so a missing
   directory is a hard boot failure ("SQLite Error 14: unable to open database
   file"), not a degraded start. The default site config points at the RELATIVE
   path ./data/site-localdb.db, so any site node without a pre-existing data/
   directory fails to boot. The docker rig escapes only because its volume mount
   happens to create /app/data — a coincidence that would have hidden this until
   a bare-metal or fresh deployment. This has been latent since Phase 1 made
   LocalDb:Path required; deleting S&F's EnsureDatabaseDirectoryExists here
   would have widened it. Re-established the guarantee at the layer that now
   owns the path (SiteLocalDbDirectory.Ensure, called before AddZbLocalDb) and
   pinned it with SiteLocalDbDirectoryTests. Non-vacuity is not assumed: two
   tests written against the wrong assumption failed with exactly this
   SQLite Error 14 before the fix existed.

2. Test fallout was ~7x the plan's estimate. The plan named "fixtures" in one
   project; the constructor change actually reaches 40 files across 7 test
   projects, and most used Mode=Memory;Cache=Shared — which LocalDb has no
   equivalent for, so every one had to move to a real temp file. Rather than
   copy the Phase 1 TestLocalDb fixture into 7 projects, added a shared
   tests/ZB.MOM.WW.ScadaBridge.TestSupport library (not a test project) so the
   WAL-sidecar cleanup and the "real, not stubbed" rationale live in one place.

Retargeted rather than deleted, in both directions: the S&F WAL test now asserts
against the LocalDb-backed store (WAL genuinely is LocalDb's job), while the
directory-creation test moved to Host.Tests (that guarantee is NOT LocalDb's).
SiteStorageServiceTests.Initialize_EnablesWalJournalMode got the same treatment.
DeploymentManagerMediumFindingsTests induced a persistence failure via an
unopenable path, which no longer reaches the assertion since the fixture now
throws first; it induces the same failure shape via an uninitialized store.

Verified: full solution build 0 warnings; SiteRuntime 532, Host 318,
AuditLog 355, ExternalSystemGateway 142, HealthMonitoring 97,
StoreAndForward 153 — 1597 passed, 0 failed.

Claude-Session: https://claude.ai/code/session_01BL2Vu1ESDQ9SCN4gVKkdts

src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Repositories/SiteExternalSystemRepository.cs

@@ -31,8 +31,9 @@ public class SiteExternalSystemRepository : IExternalSystemRepository
     public async Task<IReadOnlyList<ExternalSystemDefinition>> GetAllExternalSystemsAsync(
         CancellationToken cancellationToken = default)
     {
+        // Already open — SiteStorageService.CreateConnection now hands out a
+        // LocalDb-managed connection. Opening it again would throw.
         await using var connection = CreateConnection();
-        await connection.OpenAsync(cancellationToken);
 
         await using var command = connection.CreateCommand();
         command.CommandText = @"
@@ -63,8 +64,9 @@ public class SiteExternalSystemRepository : IExternalSystemRepository
     public async Task<ExternalSystemDefinition?> GetExternalSystemByNameAsync(
         string name, CancellationToken cancellationToken = default)
     {
+        // Already open — SiteStorageService.CreateConnection now hands out a
+        // LocalDb-managed connection. Opening it again would throw.
         await using var connection = CreateConnection();
-        await connection.OpenAsync(cancellationToken);
 
         await using var command = connection.CreateCommand();
         command.CommandText = @"
@@ -91,8 +93,9 @@ public class SiteExternalSystemRepository : IExternalSystemRepository
         if (system is null)
             return Array.Empty<ExternalSystemMethod>();
 
+        // Already open — SiteStorageService.CreateConnection now hands out a
+        // LocalDb-managed connection. Opening it again would throw.
         await using var connection = CreateConnection();
-        await connection.OpenAsync(cancellationToken);
 
         await using var command = connection.CreateCommand();
         command.CommandText = @"
@@ -140,8 +143,9 @@ public class SiteExternalSystemRepository : IExternalSystemRepository
     public async Task<IReadOnlyList<DatabaseConnectionDefinition>> GetAllDatabaseConnectionsAsync(
         CancellationToken cancellationToken = default)
     {
+        // Already open — SiteStorageService.CreateConnection now hands out a
+        // LocalDb-managed connection. Opening it again would throw.
         await using var connection = CreateConnection();
-        await connection.OpenAsync(cancellationToken);
 
         await using var command = connection.CreateCommand();
         command.CommandText = @"
@@ -178,8 +182,9 @@ public class SiteExternalSystemRepository : IExternalSystemRepository
     public async Task<DatabaseConnectionDefinition?> GetDatabaseConnectionByNameAsync(
         string name, CancellationToken cancellationToken = default)
     {
+        // Already open — SiteStorageService.CreateConnection now hands out a
+        // LocalDb-managed connection. Opening it again would throw.
         await using var connection = CreateConnection();
-        await connection.OpenAsync(cancellationToken);
 
         await using var command = connection.CreateCommand();
         command.CommandText = @"