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>

backend/internal/web/templates/chrome.html

@@ -29,21 +29,17 @@
 
 {{/* The action key. The icon strip on a card is unlabelled, so one permanent
      line under the tabs names every glyph. It follows the tab rather than the
-     row: the archived and finished buckets swap Archive for Restore, and a
-     finished series has no Done to offer. */}}
+     row: the archived bucket swaps Archive for Restore. */}}
 {{define "keyrow"}}
 <div class="keyrow" id="keyrow" aria-label="Action key"{{if .OOB}} hx-swap-oob="true"{{end}}>
   <span class="pair"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="#i-play"/></svg><span>Read</span></span>
   <span class="pair brass"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="#i-star"/></svg><span>Fav</span></span>
   <span class="pair"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="#i-pencil"/></svg><span>Chapter</span></span>
-  {{if or (eq .Tab "archived") (eq .Tab "finished")}}
+  {{if eq .Tab "archived"}}
   <span class="pair"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="#i-undo"/></svg><span>Restore</span></span>
   {{else}}
   <span class="pair"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="#i-box"/></svg><span>Archive</span></span>
   {{end}}
-  {{if ne .Tab "finished"}}
-  <span class="pair"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="#i-check"/></svg><span>Done</span></span>
-  {{end}}
   <span class="pair trash"><svg viewBox="0 0 24 24" aria-hidden="true"><use href="#i-trash"/></svg><span>Delete</span></span>
 </div>
 {{end}}