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>

internal/cmd/handoff.go

@@ -326,7 +326,7 @@ func buildRestartCommand(sessionName string) (string, error) {
 	// The SessionStart hook will run gt prime.
 	// Use exec to ensure clean process replacement.
 	if gtRole != "" {
-		return fmt.Sprintf("cd %s && export GT_ROLE=%s BD_ACTOR=%s && exec claude --dangerously-skip-permissions", workDir, gtRole, gtRole), nil
+		return fmt.Sprintf("cd %s && export GT_ROLE=%s BD_ACTOR=%s GIT_AUTHOR_NAME=%s && exec claude --dangerously-skip-permissions", workDir, gtRole, gtRole, gtRole), nil
 	}
 	return fmt.Sprintf("cd %s && exec claude --dangerously-skip-permissions", workDir), nil
 }