v26f.3

Apply HIGH-priority fixes from REVIEW-20260424b

- ch20: update Scala 2 REPL transcript to Scala 3 format
  (val/def prefixes on output, def signature without parens syntax)
- ch60: replace 4 dead feedproxy.google.com SE Radio links with
  working se-radio.net URLs (eps 12, 19, 29) + add ep 348 (Terrell)
- ch60: update Java 8 java.util.concurrent link to Java 21 API
- ch60: upgrade http Scala docs links to https
- all: bulk upgrade http:// to https:// for wikipedia, scala-lang,
  typelevel, martinfowler, akka, android developer domains
- ch50: fix dead benchmarksgame alioth link to current debian.net URL

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>