feat(web): add private club showcases with membership flow (v3.7.0)

Implements Issue #110: game masters can now publish sessions
exclusively to a club's private showcase, gated behind a
member application and approval flow. Adds a 4-state
publication_mode (None/Catalog/ClubOnly/Both) replacing the
binary is_public, plus a club_memberships table with
Pending/Active/Rejected/Left lifecycle and partial unique
index ensuring a single Active row per (group, player).

Highlights
- V030 migration: club_memberships, publication_mode, drop
  is_public, recreate partial indexes, portfolio_games gains
  publication_mode.
- PublicationMode enum + extensions in GmRelay.Shared.
- ISessionStore gains 12 membership/showcase methods;
  AuthorizedMembershipService owns the membership flow with
  GM-only approve/reject authorization.
- PublicClub / PublicMasterProfile / PublicSession: member-
  aware queries (ClubOnly visible only to Active members).
- New pages: MyClubMemberships (/profile/memberships) and
  ClubApplications (/group/{id}/applications).
- GroupDetails and EditSession switch from a bool toggle to
  a 4-state publication_mode selector.
- NavMenu adds Moji kluby, PublicLayout adds Kluby.

Tests: 4 new test files (PublicationMode, ClubMemberships,
AuthorizedMembershipService, ClubShowcaseSource) + updates
to PublicClubPages, AuthorizedSessionService/Portfolio
service FakeSessionStore, CampaignTemplatesNavigation.
493 tests pass.

Bump version 3.6.0 -> 3.7.0 across Directory.Build.props,
compose.yaml, deploy.yml, NavMenu.razor.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/GmRelay.Shared/Domain/PublicationMode.cs

@@ -0,0 +1,44 @@
+namespace GmRelay.Shared.Domain;
+
+public enum PublicationMode
+{
+    None,
+    Catalog,
+    ClubOnly,
+    Both
+}
+
+public static class PublicationModeExtensions
+{
+    public const string NoneValue = nameof(PublicationMode.None);
+    public const string CatalogValue = nameof(PublicationMode.Catalog);
+    public const string ClubOnlyValue = nameof(PublicationMode.ClubOnly);
+    public const string BothValue = nameof(PublicationMode.Both);
+
+    public static bool IsVisibleInCatalog(this PublicationMode mode) =>
+        mode is PublicationMode.Catalog or PublicationMode.Both;
+
+    public static bool IsVisibleToClubMembers(this PublicationMode mode) =>
+        mode is PublicationMode.ClubOnly or PublicationMode.Both;
+
+    public static string ToDatabaseValue(this PublicationMode mode) =>
+        mode switch
+        {
+            PublicationMode.None => NoneValue,
+            PublicationMode.Catalog => CatalogValue,
+            PublicationMode.ClubOnly => ClubOnlyValue,
+            PublicationMode.Both => BothValue,
+            _ => throw new ArgumentOutOfRangeException(nameof(mode), mode, "Unknown publication mode.")
+        };
+
+    public static PublicationMode FromDatabaseValue(string? value) =>
+        value switch
+        {
+            null or "" => PublicationMode.None,
+            NoneValue => PublicationMode.None,
+            CatalogValue => PublicationMode.Catalog,
+            ClubOnlyValue => PublicationMode.ClubOnly,
+            BothValue => PublicationMode.Both,
+            _ => throw new ArgumentOutOfRangeException(nameof(value), value, "Unknown publication mode.")
+        };
+}

src/GmRelay.Shared/Features/Showcase/ShowcaseSessionDto.cs

@@ -18,5 +18,7 @@ public sealed record ShowcaseSessionDto(
     int WaitlistedPlayerCount,
     bool AllowDirectRegistration,
     string? Description,
+    string PublicationMode = "None",
+    bool IsMembersOnly = false,
     string? MasterProfileSlug = null,
     string? MasterDisplayName = null);