Spec #136: Finished belongs to the Series — owner-owned poll gate, Lifecycle bucket dropped (#163)

Closes #136.

Spec #136 end to end: `finished` becomes a fact about the Series, written only by the owner, and the reader-facing Lifecycle bucket is gone.

## What landed

- **#157** — `series.finished_at bigint NOT NULL DEFAULT 0` plus the migration whose statement order is load-bearing (seed from the buckets, then flip them); both Lane queries lose the `HAVING COUNT(*) FILTER (WHERE b.status <> 'finished')` clause and gate on `finished_at = 0` instead, with the due-query/eligible-count force asymmetry kept deliberate and commented; `StatusFinished`, its API special-case 400, the web tab and the templates' Finished bucket deleted.
- **#158** — owner Finish control on the Series detail page: confirm-gated finish, instant un-finish, admin accent (never ember, nothing is destroyed), `Store.SetSeriesFinished`, the two routes behind the owner gate, and the state displayed on the list row without offering the control there.
- **#160** — reader side: derived `finished` bool on the flat Bookmark (`s.finished_at > 0`), rendered as a text-only label in both userscripts and on the web card; read-only inbound by omission from `Upsert`'s explicit `series` column list, same mechanism that already protects `cover`.
- **#161** — glossary and the stale Reader-count divergence note catch up.
- **#159** — `finished` joins the admin filter vocabulary (predicate `finished_at > 0`, label `Finished`, own aggregate count, figure last in the stats block as informational); the four clock-driven hygiene predicates (stale, never-checked, no-cover, no-chapter) exclude finished Series while unpollable, orphan and sighting-raised deliberately do not.

## Verification

`go vet ./...` and `go test ./...` green on the merged branch (Docker-backed, throwaway `postgres:17-alpine` per package). Each ticket also passed a two-axis review (spec + standards) on its own branch before merge.

Reviewed-on: #163
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

README.md

@@ -218,10 +218,10 @@ desktop for faster testing — install the same file unchanged.
   keeps checking it for new chapters, so it is worth coming back to. Archiving
   does not touch read progress, and reading an archived series leaves it
   archived.
-- **Finished**: series you have completed live in a **Finished** tab in the web
-  UI only. It is set there and nowhere else — the API rejects the value — and
-  finished series are hidden from every userscript tab and are no longer polled
-  for new chapters.
+- **Finished**: the owner marks a Series finished from its detail page; the
+  backend stops polling it, and every Reader sees a read-only label. It is a
+  fact about the Series, not a Reader's bucket: old `Finished` bookmarks were
+  folded into Archived in the cutover, so there is no Finished tab.
 - Bookmarks made on Asura appear when the panel is opened on Demonic, and vice
   versa — the backend is the shared store.