feat(commons): add IAuditLogRepository + AuditLogQueryFilter + AuditLogPaging (#23)

Append-only data-access surface for the central AuditLog table — three
methods: InsertIfNotExistsAsync (first-write-wins on EventId), QueryAsync
(filter + keyset paging on (OccurredAtUtc desc, EventId desc)), and
SwitchOutPartitionAsync (M1 honest contract — throws NotSupported until
M6 lands the non-aligned-index drop/rebuild dance for the partition
switch). No Update, no row-delete; bulk purge is partition-only.

Bundle D of the Audit Log #23 M1 Foundation plan.

src/ScadaLink.Commons/Types/Audit/AuditLogPaging.cs

@@ -0,0 +1,13 @@
+namespace ScadaLink.Commons.Types.Audit;
+
+/// <summary>
+/// Keyset paging cursor for <see cref="ScadaLink.Commons.Interfaces.Repositories.IAuditLogRepository.QueryAsync"/>.
+/// The repository orders by <c>(OccurredAtUtc DESC, EventId DESC)</c>; callers pass
+/// the last row of the previous page back as <see cref="AfterOccurredAtUtc"/> +
+/// <see cref="AfterEventId"/> to fetch the next page. Both must be non-null together,
+/// or both null (first page).
+/// </summary>
+public sealed record AuditLogPaging(
+    int PageSize,
+    DateTime? AfterOccurredAtUtc = null,
+    Guid? AfterEventId = null);

src/ScadaLink.Commons/Types/Audit/AuditLogQueryFilter.cs

@@ -0,0 +1,21 @@
+using ScadaLink.Commons.Types.Enums;
+
+namespace ScadaLink.Commons.Types.Audit;
+
+/// <summary>
+/// Filter predicate for <see cref="ScadaLink.Commons.Interfaces.Repositories.IAuditLogRepository.QueryAsync"/>.
+/// Any field left <c>null</c> means "do not constrain on that column". Time bounds
+/// are half-open in the spec sense — <see cref="FromUtc"/> is inclusive and
+/// <see cref="ToUtc"/> is inclusive of the upper bound; the repository SQL uses
+/// <c>&gt;=</c> / <c>&lt;=</c> respectively. All filter fields are AND-combined.
+/// </summary>
+public sealed record AuditLogQueryFilter(
+    AuditChannel? Channel = null,
+    AuditKind? Kind = null,
+    AuditStatus? Status = null,
+    string? SourceSiteId = null,
+    string? Target = null,
+    string? Actor = null,
+    Guid? CorrelationId = null,
+    DateTime? FromUtc = null,
+    DateTime? ToUtc = null);