feat: loading skeleton on the manga detail page

The detail loader now streams its six-call bundle instead of blocking
navigation on it. The page component is a thin {#await} wrapper: it shows a
MangaDetailSkeleton (cover + meta + chapter rows) while the bundle loads,
renders the extracted DetailView once resolved, and shows an inline
not-found on a 404 (previously the framework error page). Extracting
DetailView also makes it remount per navigation, so its tag/bookmark/reaction
state re-seeds cleanly on manga-to-manga moves.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/Cargo.lock

@@ -1558,7 +1558,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.121.0"
+version = "0.122.0"
 dependencies = [
  "anyhow",
  "argon2",

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.121.0"
+version = "0.122.0"
 edition = "2021"
 default-run = "mangalord"