refactor(series): drop the TS rendering twin; library switch navigates SSR

web/src/series.ts carried a full TypeScript twin of the templ page —
cards and paginator rendered via innerHTML from /api/series JSON,
always hardcoded to page 1. Combined with the header restore dispatch
(previous commit) it made every /series load stomp server-rendered
pagination back to page 1, which is the paginator bug reported on prod
(9 pages of series, Next kept landing on page 1, per-library only).

Rendering ownership (AGENTS.md): this page now has NO client renderer.
- grid and paginator are rendered only by templates/series.templ
- a library switch is a plain SSR navigation to
  /series?library_id=...&page=1, keeping the URL the single source of
  truth for both library and page state
- drops the duplicate /api/series fetch that ran on every page load

rendering-allowlist.txt: series.ts baseline entry removed — the file
no longer builds HTML anywhere.

web/src/rendering-allowlist.txt

@@ -20,7 +20,6 @@ web/src/dom.ts:1
 web/src/password_validation.ts:1
 web/src/queue.ts:3
 web/src/search.ts:4
-web/src/series.ts:1
 web/src/setup.ts:1
 web/src/stats.ts:9
 web/src/toast.ts:2