feat(dashboard): Interventions page improvements and action-confirm modal

- Move Interventions under Workstreams in the navigator
- Add action-confirm.js: shared modal component for actions requiring a
  mandatory comment (survives live-poll re-renders, unlike inline DOM mutation)
- Wire action-confirm into Interventions (Mark done) and Decisions (Resolve)
- Fix Interventions completed section: fetch all tasks and filter client-side
  so resolved interventions (needs_human=false) still appear under Completed
- Add docs/interventions.md help page with ? button on the h1
- Replace all hardcoded "Bernd" with "human" across dashboard src and docs

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

dashboard/src/docs/workstreams.md

@@ -84,7 +84,7 @@ create_workstream(
   title       = "Build user authentication",
   description = "JWT-based auth, refresh tokens, middleware",
   status      = "active",
-  owner       = "Bernd",
+  owner       = "human",
   due_date    = "2026-04-01"
 )
 ```