briar smoke test #2: closes #26

[iklobato]

Summary

End-to-end smoke test of the briar agent-crew backend.

This PR was created by chaining three briar tool invocations:

1. github.open_issue → opened the linked issue
2. github.commit_files → created branch briar/smoke-1778801767 and committed a marker file
3. github.open_pr → opened this PR

Closes #26.

What it exercises

• secrets_vault — GITHUB_TOKEN fetched from the encrypted vault and injected as token= kwarg by wrap_tool
• tool registry — three different impls (github.open_issue, github.commit_files, github.open_pr) resolved from apps.crew_runtime.tools_github
• side-effect classification — all three are mutate, so the retry wrapper deliberately did not auto-retry on errors
• CLI Docker wrapper — all three invocations went through ./bin/briar tool invoke which runs inside the project's web container

Safe to close without merging.