koi: swap the sakura panels for a shoal of letter-drawn koi

Five varieties (kohaku, ogon, sanke, showa, tancho) swim in the side
margins, drawn the way the reference does it: every cell is a filled tile
in the koi's colour with a letter punched into it in near-black, picked
from a thin-to-thick ramp by how dense that part of the body is. The tile
carries the colour, the letter carries the texture.

The grid is square and the geometry is in pixels, snapping to cells only
when one is written. Laying the body out in grid cells instead makes its
proportions depend on heading -- thickness is perpendicular to travel, so
on the natural text grid a fish swimming sideways came out short and fat
while one swimming up came out slim.

The body is a follow-the-leader chain with a bend limit per joint. A spine
projected from the head rotates rigidly the moment the fish turns, and a
raw position trail coils into a ball; the chain lags and the bend cap
keeps it from curling. Swimming comes from the head yawing with the tail
beat, which the chain propagates as a travelling wave.

Tails dissolve into loose tiles toward the tip, and the panels carry a 1em
cell grid so the motion reads against something.

Drops the sakura wiring: no art.php parse, no sideart.php stylesheet, no
<pre> layers, and the inlined sideart @font-face goes with them (-6.9 KB
of base64 from style.css). art.php, sideart.php, sakura.ans and the woff2
are left on disk, now unreferenced.

inc/footer.php

@@ -10,7 +10,8 @@ $build = preg_match('/[0-9a-f]{7,40}/i', $build, $m) ? $m[0] : ($build ?: 'dev')
   </div>
   <small>&copy; <?= date('Y') ?> · build: <a href="<?= htmlspecialchars(REPO_URL . ($build !== 'dev' ? '/src/commit/' . $build : '')) ?>"><?= htmlspecialchars($build) ?></a></small>
 </footer>
-<pre class="side side-left" aria-hidden="true"><?= str_repeat('<b></b>', $artLeft) ?></pre>
-<pre class="side side-right" aria-hidden="true"><?= str_repeat('<b></b>', $artRight) ?></pre>
+<canvas class="koi koi-left" aria-hidden="true"></canvas>
+<canvas class="koi koi-right" aria-hidden="true"></canvas>
+<script src="/js/koi.js?v=<?= filemtime(__DIR__ . '/../js/koi.js') ?>" defer></script>
 </body>
 </html>

inc/header.php

@@ -1,7 +1,5 @@
 <?php
 require_once __DIR__ . '/../config.php';
-require_once __DIR__ . '/art.php';
-[$artCss, $artLeft, $artRight] = ansi_css_cached(__DIR__ . '/art/sakura.ans');
 ?>
 <!doctype html>
 <html lang="en">
@@ -12,7 +10,6 @@ require_once __DIR__ . '/art.php';
   <title><?= htmlspecialchars($page_title ?? SITE_TITLE) ?></title>
   <link rel="icon" href="/img/favicon.ico" sizes="any">
   <link rel="stylesheet" href="/css/style.css?v=<?= filemtime(__DIR__ . '/../css/style.css') ?>">
-  <link rel="stylesheet" href="/sideart.php?v=<?= filemtime(__DIR__ . '/art/sakura.ans') . '-' . filemtime(__DIR__ . '/art.php') ?>">
   <script src="/js/htmx.min.js" defer></script>
   <script src="/js/idiomorph-ext.min.js" defer></script>
 </head>