Link branch views to their GitHub PRs

[srid]

Branch and job pages now show a direct GitHub PR link when the branch has one. Vira derives the GitHub repository from the configured clone URL, asks gh pr list for a matching head branch, and renders a compact external PR button beside the existing page actions.

The lookup keeps the no-PR, unsupported-repo, and failed-lookup states separate. To avoid shelling out on every page load, branch PR lookups now go through a bounded in-process cache: entries live for 60 seconds, are keyed by clone URL plus branch, and are capped at 256 entries. Failed fresh lookups are logged; cached failures stay quiet.

This also records the project rule to never force push and never rebase in the APM source instructions, with generated agent files refreshed through just apm.

Verified

nix develop -c cabal build all
nix develop -c cabal run gh-test
nix develop -c cabal run git-effectful-test
nix develop -c cabal run vira-tests
nix develop -c hlint packages/vira/src/Vira/Web/PullRequestCache.hs packages/vira/src/Vira/App/Type.hs packages/vira/src/Vira/App/Run.hs packages/vira/src/Vira/Web/Widgets/Commit.hs packages/vira/test/Vira/Web/PullRequestCacheSpec.hs

Try it locally

nix run github:juspay/vira/unholy-load

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