fix(frontend): reader back button pops history instead of pushing (0.60.2)

The reader's "back to manga" link was a naked `<a href="/manga/{id}">`
that pushed a new history entry on every tap, so browser-back kept
ping-ponging between detail and reader instead of walking out to
home:

  home → detail → reader → reader-back (push detail) → detail-back
       (pop reader) → reader-back (push detail) → … loop forever

The fix intercepts left-click and calls `window.history.back()`
directly when there's same-tab history to pop. Middle-click /
cmd-click / right-click pass through so "open in new tab" still
works, and a deep-link / fresh-tab visit where `history.length ===
1` falls through to the href so the button still leads somewhere
useful.

An earlier attempt gated the back on
`document.referrer.startsWith(origin)` — but SvelteKit's SPA
`pushState` doesn't update `document.referrer`, so that check was
always false in practice and the default href fired anyway. The
e2e regression added here uses real link clicks (not
`window.location.href`) so it actually exercises the SPA-nav path
the bug lives on.

Verified: home → detail → reader, then reader-back keeps
`history.length` at 4 (popped, not pushed), and a second tap on the
detail back button walks out to /.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/Cargo.lock

@@ -1470,7 +1470,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.60.1"
+version = "0.60.2"
 dependencies = [
  "anyhow",
  "argon2",

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.60.1"
+version = "0.60.2"
 edition = "2021"
 default-run = "mangalord"