Atlas modal: pose toggle + wiki descriptions

avian/api/cutout.php: read ?pose=N parameter. pose=1 (default) serves
<slug>.png, pose=2 serves <slug>-2.png, etc. Pose >1 missing falls
back to pose-1 instead of skipping to the photo cutout so the flight
tab still shows something recognisable. Pose clamped to 1-99 to
block path-traversal payloads.

avian/api/wiki.php (new): Wikipedia REST summary proxy. Returns
{extract, thumbnail, title}. Thumbnail host pinned to wikimedia.org/
wikipedia.org to block SSRF. Cached for 24h.

avian/frontend/apt.js: fetch wiki descriptions from ./avian/api/wiki.php
(was hitting the worker's /api/wiki.json which 404'd in our overlay).

avian/frontend/apt.js

@@ -1856,7 +1856,7 @@
     // Wikipedia summary (description + genus / family).
     var loadWiki = WIKI_CACHE[sci]
       ? Promise.resolve(WIKI_CACHE[sci])
-      : fetchJson('/api/wiki.json?sci=' + encodeURIComponent(sci)).then(function (j) {
+      : fetchJson('./avian/api/wiki.php?sci=' + encodeURIComponent(sci)).then(function (j) {
           WIKI_CACHE[sci] = j; return j;
         });
     loadWiki.then(function (j) {