Docs, README, launchers, PWA install

Milestone 7. docs/MODULE-GUIDE.md documents the whole module contract
from an author's point of view — manifest reference, client factory +
moduleApi, server init/routes/health, scoping and resilience rules, a
copy-paste minimal module, and a testing section with the two mocks and a
resilience checklist. README rewritten with run/configure/use
instructions in the prodcom-listener style, plus double-click launchers
for macOS and Windows. PWA: manifest, icons, and a minimal network-first
service worker that never touches /api/*.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RNYUv9EyrGSFmCnmH7WYKH

public/admin/index.html

@@ -5,6 +5,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <title>ProdDash Admin</title>
   <meta name="theme-color" content="#0b0e12">
+  <link rel="icon" href="/icons/icon-192.png">
   <link rel="stylesheet" href="/style.css">
   <link rel="stylesheet" href="/admin/admin.css">
 </head>