Everything in UI5

Not behind a managed approuter: SAP Build Work Zone does not expose the `/$companion/**` routes, so Companion never reaches CAP, and the README names managed approuter and Work Zone as out of scope for v1. Not where help has to be authored in a browser, since the editor, the producer and writes are absent and content lives in files the plugin compiles.

It is text processing, not an agent: there is no tool calling, no retrieval and no conversation. It needs SAP AI Core, and the backend half needs [@sap-ai-sdk/orchestration](artifact:sap-ai-sdk-orchestration) installed alongside it — an optional peer, so a frontend-only install stays lean.