Set GIT_AUTHOR_NAME per agent session (gt-6r18e.1)

Export GIT_AUTHOR_NAME alongside BD_ACTOR in all agent session startup
locations. This enables git log --author queries for agent work while
keeping GIT_AUTHOR_EMAIL as the workspace owner.

Files updated:
- internal/session/manager.go (polecat sessions)
- internal/daemon/daemon.go (deacon, witness, polecat via daemon)
- internal/daemon/lifecycle.go (polecat lifecycle)
- internal/cmd/*.go (crew, mayor, deacon, witness, refinery, up, handoff)
- internal/session/manager_test.go (updated test expectations)
- docs/federation.md (marked feature as implemented)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/federation.md

@@ -155,7 +155,7 @@ bd audit --actor=gastown/crew/joe
 
 ## Implementation Status
 
-- [ ] Agent identity in git commits
+- [x] Agent identity in git commits
 - [ ] BD_ACTOR default in beads create
 - [ ] Workspace metadata file
 - [ ] Cross-workspace URI scheme