net dashboard: load node diagnostics only on explicit action

[Patrick W. Healy (phealy)]

Purpose

Switch dashboard streams to overview state and connect node dialogs to explicit Load data/Refresh actions. Selection, reconnect, and summary updates no longer request or subscribe to node details.

Compatibility

Based on #780, whose legacy observer makes cached diagnostics available to old full publishers without requiring direct HTTP reachability. Publishing defaults and controller bulk compatibility remain unchanged pending final activation.

Validation

14 frontend tests, TypeScript check, and Vite build passed. Immediate-parent diff: 602 added+deleted lines.

Part of the draft lightweight-status stack based on #745.

Lightweight status draft stack

Base: #745. Each layer targets the preceding branch and remains draft.

#746 -> #747 -> #748 -> #750 -> #751 -> #752 -> #753 -> #754 -> #755 -> #756 -> #757 -> #758 -> #759 -> #760 -> #761 -> #762 -> #763 -> #764 -> #765 -> #766 -> #767 -> #768 -> #769 -> #770 -> #771 -> #772 -> #773 -> #774 -> #775 -> #776 -> #777 -> #778 -> #779 -> #780 -> #781 -> #782 -> #783 -> #784 -> #785 -> #786 -> #787 -> #788 -> #789 -> #790 -> #791 -> #792 -> #793 -> #794 -> #795 -> #796 -> #797 -> #798 -> #799

[Patrick W. Healy (phealy)]

This PR was mistaken churn from splitting the lightweight-status work into unnecessarily small PRs. That was my mistake, not a requirement from the user.

Its changes are preserved in #766 within the user-approved, consolidated 12-PR draft stack. Closing this superseded PR; the implementation is not being discarded, and nothing has been merged into main.