feat(hyperguild): tier subcommand

Adds the tier subcommand to the hyperguild CLI. Reuses
internal/tier.Detect verbatim, sources probe URLs from
ANTHROPIC_PROBE_URL (default https://api.anthropic.com) and
LITELLM_BASE_URL (no default — empty triggers airplane).

Human-readable output by default; --json emits the same Info struct
as the supervisor's tier MCP returns. Tests cover all three tier
states via httptest fakes.

cmd/hyperguild/main.go

@@ -25,7 +25,7 @@ func notYet(ctx context.Context, args []string, stdin io.Reader, stdout, stderr
 
 func subcommands() map[string]subcommand {
 	return map[string]subcommand{
-		"tier":  notYet,
+		"tier":  runTier,
 		"brain": notYet,
 		"mode":  notYet,
 	}