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/decisions.md

@@ -105,7 +105,7 @@ Any `pending` decision whose title or rationale contains financial or legal keyw
 - Sort to the top of the list
 - Carry an amber escalation note explaining the reason
 - Trigger the warning box at the bottom of the page listing all escalated items
-- **Must be reviewed and approved by Bernd before any related action is taken (constitution §4)**
+- **Must be reviewed and approved by the human before any related action is taken (constitution §4)**
 
 To clear an escalation, resolve the decision via `resolve_decision()` in the MCP server or the REST API.