feat: Expose branch.base_ref and branch.ref_type to env variables

[Vitor-Avila]

Summary

Exposing branch's base_ref and ref_type as environment variables that can be used in .agor.yml files.

Why / context

This is pretty useful to orchestrate environment deployment through Codespaces with Agor. When you create a new branch in Agor, that branch doesn't yet exist upstream. That said, trying to spin up Codespaces would fail. This feature allows to configure the env to start pointing to the base branch (that exists upstream). For example:

gh cs create -R "$REPO" -b "$BASE_BRANCH" -d "$DISPLAY" \
  --devcontainer-path "$DEVCONTAINER" \
  -l "$LOCATION" -m "$MACHINE" \
  --idle-timeout "$IDLE_TIMEOUT" --retention-period "$RETENTION" \
  --default-permissions

Implementation notes

Might not be super widely adopted, but not a big change either. Just expanding the existing framework.

Validation / test plan

• pnpm test
• pnpm typecheck
• Manual validation

Screenshots / demos

No meaningful UI changes.

Risks / rollout / rollback

No risks.

Out of scope / follow-ups

Thought about using the {{custom.*}} branch properties. It doesn't have a native UI editor, so you must go through MCP change. Also feels like a natural feature.

[richardfogaca]

LGTM