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.

ui/e2e/social.spec.ts

@@ -193,6 +193,29 @@ test('game: the add-friend 🤝 confirms with a tap and then reads as sent', asy
   await expect(add).toBeDisabled();
 });
 
+test('game: the block ✖️ confirms in red, then hides both controls and strikes the name', async ({ page }) => {
+  await loginLobby(page);
+  await page.getByRole('button', { name: /Ann/ }).click(); // active game vs Ann
+  await page.locator('.scoreboard').click(); // open the history -> 🤝 and ✖️ appear on Ann's card
+  const block = page.getByRole('button', { name: 'Block player' });
+  await expect(block).toBeVisible();
+  await block.click(); // arm: ✖️ -> a fading ✅, the score caption turns to a red "Block?"
+  await expect(page.locator('.sc.blockprompt')).toHaveText('Block?');
+  // While confirming a block the add-friend control is hidden so the two never overlap.
+  await expect(page.getByRole('button', { name: 'Add to friends' })).toHaveCount(0);
+  await block.click(); // confirm within the window
+  // The block applied (optimistically): both controls disappear and the name is struck.
+  await expect(page.getByRole('button', { name: 'Block player' })).toHaveCount(0);
+  await expect(page.getByRole('button', { name: 'Add to friends' })).toHaveCount(0);
+  await expect(page.locator('.nm.struck')).toBeVisible();
+
+  // The chat composer is hidden for a blocked opponent — only the log remains, as in a
+  // finished game.
+  await page.getByRole('button', { name: 'Chat' }).click(); // 💬 -> comms hub
+  await expect(page.getByRole('button', { name: 'Send' })).toHaveCount(0);
+  await expect(page.getByRole('button', { name: 'Nudge' })).toHaveCount(0);
+});
+
 test('game: an opponent who is already a friend shows no add-friend 🤝', async ({ page }) => {
   await loginLobby(page);
   await page.getByRole('button', { name: /Kaya/ }).click(); // finished game vs Kaya, a seeded friend