feat(social): asymmetric per-user block, in-game block control, admin lists

Make a per-user block one-directional and non-destructive: the blocker stops
receiving everything from the blocked user (chat, nudge, friend requests,
invitations) and the matchmaker never pairs them, while the blocked user
notices nothing — their sends still persist by the normal rules but are never
delivered or surfaced (born-read). A block no longer deletes the friendship
(an unblock cleanly restores it) and instant-reads any unread the blocked user
had left for the blocker.

- backend: a directional blockExists guard across chat/nudge/friends/invitations
  (store-but-hide for the blocked->blocker direction, refuse blocker->blocked);
  the matchmaker excludes a block-related pair (both directions) from auto-match;
  user_blocked/user_unblocked notifications to the blocker only (in-app only).
- ui: the opponent score card gains a block ✖️ control mirroring add-friend
  (red "Block?" confirm, mutual-hide while confirming, struck name, hidden chat
  composer when blocked); optimistic apply + event confirm + rollback for both.
- admin: the user card gains cross-linked blocks / blocked-by / friends lists.
- docs: FUNCTIONAL(+ru), ARCHITECTURE §10 + decision record, UI_DESIGN, PRERELEASE.

backend/internal/adminconsole/templates/pages/user_detail.gohtml

@@ -102,6 +102,36 @@
 </tbody>
 </table>
 </section>
+<section class="panel"><h2>Friends</h2>
+<table class="list">
+<thead><tr><th>Account</th><th>Friends since</th></tr></thead>
+<tbody>
+{{range .Friends}}
+<tr><td><a href="/_gm/users/{{.AccountID}}">{{.DisplayName}}</a></td><td>{{.Date}}</td></tr>
+{{else}}<tr><td colspan="2"><span class="note">no friends</span></td></tr>{{end}}
+</tbody>
+</table>
+</section>
+<section class="panel"><h2>Blocks</h2>
+<table class="list">
+<thead><tr><th>Account</th><th>Blocked at</th></tr></thead>
+<tbody>
+{{range .Blocks}}
+<tr><td><a href="/_gm/users/{{.AccountID}}">{{.DisplayName}}</a></td><td>{{.Date}}</td></tr>
+{{else}}<tr><td colspan="2"><span class="note">blocks no one</span></td></tr>{{end}}
+</tbody>
+</table>
+</section>
+<section class="panel"><h2>Blocked by</h2>
+<table class="list">
+<thead><tr><th>Account</th><th>Blocked at</th></tr></thead>
+<tbody>
+{{range .BlockedBy}}
+<tr><td><a href="/_gm/users/{{.AccountID}}">{{.DisplayName}}</a></td><td>{{.Date}}</td></tr>
+{{else}}<tr><td colspan="2"><span class="note">blocked by no one</span></td></tr>{{end}}
+</tbody>
+</table>
+</section>
 {{if .TelegramID}}
 <section class="panel"><h2>Send Telegram message</h2>
 {{if .ConnectorEnabled}}