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/progress-log.md

@@ -64,7 +64,7 @@ Every Claude Code session working in this repository should:
 1. **Start** — call `get_state_summary()` for orientation
 2. **End** — call `add_progress_event()` to log what was done, decided, or discovered
 
-A session that produces no progress events is invisible to future sessions and to Bernd. The log is how continuity is maintained across context windows.
+A session that produces no progress events is invisible to future sessions and to the human. The log is how continuity is maintained across context windows.
 
 ---
 
@@ -87,7 +87,7 @@ Via the REST API directly:
 ```bash
 curl -X POST http://127.0.0.1:8000/progress/ \
   -H "Content-Type: application/json" \
-  -d '{"summary": "…", "event_type": "note", "author": "Bernd"}'
+  -d '{"summary": "…", "event_type": "note", "author": "human"}'
 ```
 
 ---
@@ -96,7 +96,7 @@ curl -X POST http://127.0.0.1:8000/progress/ \
 
 | Filter | Effect |
 |---|---|
-| **Author** | Restrict to events by a specific author (`custodian`, `Bernd`, etc.) |
+| **Author** | Restrict to events by a specific author (`custodian`, `human`, etc.) |
 | **Event type** | Restrict to one category of event |
 | **Since** | Show only events after a chosen date |