fix(browser): an unresolvable collection redirects to the top, not its bare root

[ajslater]

Summary

A browse route whose collection pk resolves to nothing redirected to that collection's own bare root (e.g. /series), not the top collection's root. Under a Publishers top collection, that page is a dead end:

• the backend sends only the root crumb,
• breadcrumbs.vue hides the last crumb because it's the current view, and its "Top" fallback only fires when parentIds exist, so nothing shows,
• / resumes the saved last route, which is now /series, so the user stays stuck until they switch top collections.

How it was hit

Tag a comic while viewing its series or volume. If the tag write moves the comic(s) elsewhere, the old group is left empty. The next library.changed refresh probes /head, the count changes, and the page reloads. The full ACL resolves through comic__, so the emptied group no longer resolves, and the redirect (added in #902) sent the user to /series.

Change

_raise_unresolved_collection_redirect now reuses _get_up_page_redirect() from page_in_bounds.py, the same target the out-of-bounds page redirect already uses:

• the top collection's root (serialized as publishers with no parent ids) for the publisher hierarchy and comics,
• the folders or story arcs root in those views, unchanged.

Tests

• test_a_pk_that_names_nothing_redirects_to_the_top: now expects publishers instead of series.
• test_an_emptied_volume_redirects_to_the_top: new. It moves a volume's only comic out, as a tag write would. Both of these fail on the old code and pass with the fix.
• The stamped-folder test now also asserts the redirect stays in folders.
• make fix, make lint, make ty and make test all pass: Python 1569 passed (1 xfailed), frontend 940 passed.
• Checked by hand in the dev server: /series/999999 lands on /publishers with Top Collection "Publishers".

Reviewer notes

• make lint reports two reportUnreachable warnings in codex/views/browser/annotate/cover.py. That file isn't touched here; the warnings were already there.
• A separate follow-up covers two frontend paths that may reach the same stranded state: clearing a search with the empty-results "Clear Filters and Search" button (clearFilters(true) skips _validateSearch), and loadSavedSettings dropping its redirect.

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