Add animekai source with 1anime direct-MP4 backend (independent CDN)

animekai.be fronted two server backends per episode: megaplay.buzz
(same player/CDN family as hianime — 403s our egress IP) and
my.1anime.site (direct progressive MP4, independent CDN — verified
serving our IP at ~2.4MB/s). This is the rescue path around the
MegaPlay Cloudflare block, per the ani-cli #1945/#1918 work.

- providers/animekai.py: standard interface, per-episode backend
  dispatch (1anime first, then megaplay), same listed-but-dead ->
  raise semantics as hianime. All endpoints ride the shared TTL cache
  (no re-fetching on repeat UI hits).
- upstream.py: megaplay_master() moved out of hianime — the MegaPlay
  chain (embed -> data-id -> getSourcesNew -> enc decrypt -> CDN proof)
  is now shared by every provider fronting that player.
- app.py: /stream forwards Range for progressive files (206 +
  Content-Range passthrough, partial bodies never LRU-cached, 8MB cap
  on the parallel path so a 250MB MP4 can't pin RAM). api_stream
  reports hls=true/false from the URL — the player kind is a property
  of the URL, so future stream types slot in without app changes.
- app.js: hls===false -> native <video> (existing Range-seeking),
  hls.js path untouched.
- run.sh: ANI_SOURCE=animekai,hianime,anidb,anikoto (revert to the old
  chain when the MegaPlay block lifts).
- tests: test_animekai.py (offline: interface, enc decrypt, /stream
  Range via monkeypatched network) + test_animekai_live.py (opt-in
  ANI_LIVE=1 end-to-end, skipped by default so the suite never touches
  animekai.be).

static/app.js

@@ -1138,7 +1138,11 @@ async function play(ep_id, ep_no) {
         branch: (!window.Hls || !Hls.isSupported()) ? (nativeOK !== "none" && nativeOK !== "" ? "native" : "none-throw") : "hlsjs",
         hls_lib: typeof window.Hls, mse, native_hls: nativeOK, ua: navigator.userAgent});
     } catch {}
-    if (!window.Hls || !Hls.isSupported()) {
+    if (s.hls === false) {
+      // progressive file (1anime's direct MP4): native <video>; the /stream
+      // proxy forwards the browser's Range requests, so seeking works
+      v.src = "/stream/" + s.token;
+    } else if (!window.Hls || !Hls.isSupported()) {
       // No MSE (e.g. iOS < 17): fall back to the browser's NATIVE HLS player.
       // iOS Safari plays standard m3u8 in <video> directly — same proxied URL,
       // same-origin, so no CORS needed.