fix(crawler): walk list pages incrementally; stop on empty page (0.45.1)

The pre-built `1..=parse_last_page` queue silently broke whenever the
configured CRAWLER_START_URL lacked a `/N/` path segment: page_url
returned the input unchanged, every "next" page re-fetched page 1, and
the dedup set caught the duplicates as a flood of "skip already-seen
key in this run" debug lines. The walker now increments next_page on
each batch and terminates when parse_manga_list_from yields an empty
list (the `#logo` sentinel still converts unrendered pages into
transient errors, so an Ok(vec![]) is a real end-of-index signal).

parse_last_page and build_page_order are deleted along with their
unit tests; they have no callers under the new model. page_url and
the page-1 HTML cache from discover() are retained as-is.

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

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.45.0",
+  "version": "0.45.1",
   "private": true,
   "type": "module",
   "scripts": {