fix(github): keep merged PRs as branch history instead of hiding them

Branch status resolves an open PR across the whole fork network first, so a
merged fork PR can never hide an open upstream PR for the same head. Only when
no target has an open PR does the branch's newest closed/merged PR come back,
as history.

The panel shows that history as a compact note and offers creating the next PR
below it, instead of either sticking on a terminal PR or going blank after a
merge. Terminal associations stay persisted for reload continuity but are never
treated as authority: they revalidate on the discovery cadence and on focus.

History is looked up only for the branch's own remote and name, and remembered
per repo+branch, so the extra lookup cannot exhaust the route's resolve budget.
The checks summary and merge-permission lookup are skipped for a closed or
merged PR, where neither is actionable.

packages/ui/src/lib/i18n/messages/es.ts

@@ -998,6 +998,8 @@ export const dict: Record<I18nKey, string> = {
   "gitView.pr.field.draft": "Borrador",
   "gitView.pr.field.title": "Título",
   "gitView.pr.githubNotConnected": "GitHub no está conectado",
+  "gitView.pr.history.merged": "La PR #{number} se fusionó en {base}.",
+  "gitView.pr.history.closed": "La PR #{number} se cerró.",
   "gitView.pr.loadingDescription": "Cargando descripción...",
   "gitView.pr.mergeMethod.merge": "Crear un merge commit",
   "gitView.pr.mergeMethod.rebase": "Rebase y merge",