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.Web/Components/Layout/PublicLayout.razor

@@ -6,7 +6,10 @@
             <img src="/logo.png" alt="GM-Relay" />
             <span>GM-Relay</span>
         </a>
-        <a class="btn-gm btn-gm-outline" href="/login">Войти</a>
+        <div class="public-topbar-actions">
+            <a class="btn-gm btn-gm-outline" href="/showcase">Клубы</a>
+            <a class="btn-gm btn-gm-outline" href="/login">Войти</a>
+        </div>
     </header>
 
     <main class="public-content">