[Djuuu]

Summary

• Add context-graph.exclude, a git config multivar of fully-qualified ref glob patterns
  (refs/heads/..., refs/tags/..., refs/remotes/...) to always exclude from the graph.

  Injected as git log --exclude=<pattern> ahead of every --all/--branches/--tags/
  --remotes/--glob option, stripping the namespace prefix as each of those requires.
  Patterns not scoped to a specific namespace (e.g. using **) apply across all of them.

• --config-reset now also reports and clears context-graph.exclude, matching its
  documented "remove all context-graph configuration" behavior (it previously only handled
  branch context and the first-parent preference).

• Document both context-graph.exclude and context-graph.first-parent in a new
  CONFIGURATION section (--usage and README).

• Minor test cleanup: drop --pretty=oneline / git config --local where redundant.