docs: add licensing programme specs

Seven specs covering the licensing and billing programme:

- 0a shared-module: extract shared Go module, remove sitesvc duplication
- 0b instance-rename: Org -> Instance, including the database field
- 1  licensing-core: lk-signed licence payload, offline verify, CLI issuer
- 2  instance-licensing: storage, enforcement, degraded mode, settings UI
- 3  admin-backend: accounts, instances, licences, subscriptions, injection
- 4  admin-site: staff and customer portal
- 5  paddle-billing: catalog, checkout, webhooks, signup migration

Design only. No implementation.

Un-ignores docs/superpowers/ so specs are versioned.

.gitignore

@@ -2,7 +2,8 @@ node_modules
 dist
 build
 .env
-docs
+docs/*
+!docs/superpowers/
 .superpowers
 installer/vantage-agent-windows-amd64.exe
 installer/*.msi