fix: add illumos/solaris support for disk space check (#798)

Solaris/illumos use Statvfs (POSIX standard) rather than Statfs.
Add daemon_health_solaris.go and exclude illumos/solaris from the
generic unix build constraint.

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

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/daemon_health_unix.go

@@ -1,4 +1,4 @@
-//go:build !windows && !wasm && !freebsd
+//go:build !windows && !wasm && !freebsd && !illumos && !solaris
 
 package main