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/lobby/lobby.go

@@ -38,11 +38,15 @@ type RobotProvider interface {
 	PickNamed(variant engine.Variant) (uuid.UUID, string, error)
 }
 
-// Blocker reports whether two accounts have a block between them (either
-// direction). social.Service satisfies it; the lobby uses it to refuse
-// invitations between blocked accounts.
+// Blocker exposes the per-user block graph the lobby needs. social.Service satisfies it.
+// Invitations consult the exact direction (Blocks) so the inviter's block refuses while a
+// block the invitee placed on the inviter is silently suppressed; auto-match consults
+// BlockedWith so a block either way keeps the pair out of the same anonymous game.
 type Blocker interface {
-	IsBlocked(ctx context.Context, a, b uuid.UUID) (bool, error)
+	// Blocks reports whether blocker has blocked blocked (exact direction).
+	Blocks(ctx context.Context, blocker, blocked uuid.UUID) (bool, error)
+	// BlockedWith returns every account in a block with accountID in either direction.
+	BlockedWith(ctx context.Context, accountID uuid.UUID) ([]uuid.UUID, error)
 }
 
 // Auto-match defaults: a casual two-player game on the longest move clock with one