feat: allow dashboard access by GitHub team

[pilipilisbot]

Summary

• add GITHUB_AGENT_BRIDGE_DASHBOARD_ALLOWED_TEAMS for dashboard OAuth authorization
• authorize team members by matching GitHub /user/teams entries as org/team-slug
• request read:org when org or team allowlists are configured
• document the new team allowlist setting

Closes #55

Tests

• PYTHONPATH=src .venv/bin/python -m pytest tests/test_backend.py -q
• PYTHONPATH=src .venv/bin/python -m pytest -q
• git diff --check

[pilipilisbot]

Update: GitHub Actions are now green on this PR.

Checks:

• dashboard passed.
• pytest (3.11) passed.
• pytest (3.12) passed.

I also rechecked the branch locally: the worktree is clean, origin/main...HEAD contains only the intended allowed-team implementation/docs/tests delta, and git diff --check origin/main...HEAD passes.

[pilipilisbot]

Post-merge follow-up for the approval event: PR #56 has been merged and released.

Status:

• Merged via f860c7f and released as v0.20.0 at b615d43.
• Post-merge tests and release workflows both passed on main.
• Local workspace is clean on main matching origin/main; no stale issue-55-allowed-teams branch remains.

Links:

• Tests run: https://github.com/pilipilisbot/github-agent-bridge/actions/runs/26580595228
• Release run: https://github.com/pilipilisbot/github-agent-bridge/actions/runs/26580595297

[pilipilisbot]

Sync-after-merge cleanup result for PR #56:

• Confirmed the PR is merged via f860c7f and released as latest v0.20.0 at b615d43.
• Confirmed post-merge tests and release workflows passed on main.
• Fetched/pruned the local checkout; canonical workspace is clean on main matching origin/main.
• No dedicated PR feat: allow dashboard access by GitHub team #56 worktree exists, so there was nothing to remove. No stale local issue-55-allowed-teams branch is present.