docs(dashboard): add Ralph Workplan reference page

Covers installation, usage, workplan file format, task status lifecycle,
custodian naming conventions, COULOMBCORE usage, and manual cancellation.
Registered in Reference nav + reference.md index.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dashboard/observablehq.config.js

@@ -56,6 +56,7 @@ export default {
         { name: "Live Data",                path: "/docs/live-data" },
         { name: "Overview",                 path: "/docs/overview" },
         { name: "Progress Log",             path: "/docs/progress-log" },
+        { name: "Ralph Workplan",           path: "/docs/ralph-workplan" },
         { name: "Reference & Context Help", path: "/docs/reference" },
         { name: "Repo Integration",         path: "/docs/repo-integration" },
         { name: "Repos",                    path: "/docs/repos" },