Add multiplayer rooms and Vercel analytics

docs/multiplayer.md

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+# Multiplayer rooms
+
+Open a published map, select **Multiplayer**, enter your player name, and choose
+a limit from 2 to 16 players, including yourself. Create the room and copy its
+invite link. Friends open that link, enter a name, and join. The owner starts
+the match once at least two players are present and can remove players from
+the lobby.
+
+Everyone plays the same five randomly selected locations with the selected
+difficulty. A round starts when active players have loaded its images, with a
+30-second loading grace period. The timer and scoring run in PostgreSQL;
+refreshing the page restores the same player, guess, and deadline. Guesses and
+scores are revealed when everyone submits or the timer expires. Missing guesses
+score zero. The owner can advance from the round standings, or the next round
+starts automatically after 20 seconds. The final table ranks total points;
+equal totals share a place.
+
+Players join without an account. A separate HttpOnly cookie identifies each
+browser, and the room link acts as the invitation. Only the server can access
+the room tables and functions. Clients receive the current round's signed
+images and completed results, never future locations or other players' guesses
+before a round closes. Leaving the lobby frees a place; leaving during a match
+retains the player's results and scores their remaining rounds as zero. If the
+owner leaves, ownership transfers to another remaining player.
+
+Room state refreshes every two seconds, or every five seconds in a hidden tab.
+Unfinished rooms expire after 24 hours. Multiplayer results are separate from
+the solo leaderboard.
+
+## Database and verification
+
+Apply `supabase/migrations/20261007071259_multiplayer_rooms.sql` to a new database
+before deploying the web update. It has already been applied to MineGeo's
+configured Supabase project. Deployments continue through `npm run deploy`
+without a Git-provider connection.
+
+- `npm test`: validation and existing regression checks.
+- `npm run test:multiplayer`: isolated PostgreSQL state, permission, and scoring
+  checks, using the existing `.data/sql-verification` PGlite installation.
+- `node scripts/test-multiplayer-http.mjs <site-origin>`: real API and Storage
+  verification, including five-round rankings and concurrent last-slot joins.
+  Requires local Supabase configuration; creates and removes its own test rooms.
+- `node scripts/test-multiplayer-browser.mjs <site-origin>`: desktop and mobile
+  invite, reconnect, map interaction, and five-round standings checks. Requires
+  Playwright Chromium; removes its own test room and saves screenshots locally.