COMP-1520: Update token cache duration and clarify public-repo docs

[munishchouhan]

Summary

• Change default wave.tokens.cache.duration from 1h to 36h in both TokenConfig.groovy and docs/configuration.md
• Clarify wave.build.public-repo documentation to specify it is used as the target repository for freeze mode builds with packages (Conda/pip) via the v2 API when no custom buildRepository is provided, that it defaults to the
  imageSuffix naming strategy, and that its registry hostname must be unique from wave.build.repo / wave.build.cache-repo for correct credential resolution

Changed files

• src/main/groovy/io/seqera/wave/configuration/TokenConfig.groovy — default 1h → 36h
• docs/configuration.md — updated default value and expanded wave.build.public-repo description