Rebuild the web UI on Bootstrap 5 with the dark felt theme

The lobby was hand-rolled CSS and looked plain. Vendor Bootstrap 5.3
(MIT) under web/vendor so builds stay offline, load it in dark mode and
bridge the felt/gold palette onto Bootstrap's CSS variables in a new
theme.css; style.css now only owns the game table, cards and scoring
summary.

Rebuild the lobby, waiting room and shared chrome with Bootstrap
components: a shared navbar, creation form as cards with schema-driven
controls, roster as a list group with seat/team badges, a seats progress
bar and a copy-to-clipboard button on the join code. History,
leaderboard, connection/error states and the 404 page use cards, tables
and buttons too; the play table itself is unchanged.

The copy feedback timer is cancelled when the waiting room is rebuilt by
another player joining, fixing a disposed-signal panic that froze the
page mid-match.

web/index.html

@@ -1,10 +1,13 @@
 <!doctype html>
-<html lang="en">
+<html lang="en" data-bs-theme="dark">
 <head>
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <title>Tavolo</title>
     <link data-trunk rel="rust" href="Cargo.toml">
+    <!-- Bootstrap 5.3.3 (MIT), vendored so builds work offline. -->
+    <link data-trunk rel="css" href="vendor/bootstrap.min.css">
+    <link data-trunk rel="css" href="theme.css">
     <link data-trunk rel="css" href="style.css">
     <!-- Card images (CC0 woodcut napoletane deck) copied verbatim into dist. -->
     <link data-trunk rel="copy-dir" href="assets">