feat: unify Telegram and Discord accounts via identity linking

- Add V020 migration: player_links + identity_audit_log tables
- Add ISessionStore methods: ResolveEffectivePlayerId, LinkIdentity, UnlinkIdentity, GetLinkedIdentities
- Update SessionService to resolve effective player id for all permission checks
- Add /auth/discord/callback linking flow when already authenticated
- Add /api/me/identities GET/DELETE endpoints
- Add Profile.razor page for managing linked accounts
- Update NavMenu with profile link and v3.0.0 badge
- Bump version to 3.0.0 across all files

Bump version → 3.0.0

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/GmRelay.Web/Components/Layout/NavMenu.razor

@@ -34,6 +34,13 @@
                     </svg>
                     Шаблоны
                 </NavLink>
+                <NavLink class="nav-item" href="profile" @onclick="CloseMenu">
+                    <svg class="nav-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+                        <path d="M20 21v-2a4 4 0 0 0-4-4H8a4 4 0 0 0-4 4v2"/>
+                        <circle cx="12" cy="7" r="4"/>
+                    </svg>
+                    Профиль
+                </NavLink>
             </div>
 
             <div class="nav-footer">
@@ -66,7 +73,7 @@
                     </button>
                 </form>
 
-                <div class="nav-version">v2.8.1</div>
+                <div class="nav-version">v3.0.0</div>
             </div>
         </Authorized>
         <NotAuthorized>