feat: hide Devframe Inspector by default and auto-hide empty terminals/messages docks

[antfubot]

Description

Two dock-visibility changes for Vite DevTools:

• Devframe Inspector is hidden by default. The meta-introspection dock (from @devframes/plugin-inspect) no longer shows up in the dock bar out of the box. A new "Show Devframe Inspector" toggle in Settings → Advanced opts into it. Backed by a new optional showDevframeInspector field on the kit's DevToolsDocksUserSettings; the client filters the inspector out of the dock bar unless it's enabled, while still listing it in the Docks management view so it stays discoverable.

• Terminals & Messages docks auto-hide when empty. The hub's built-in ~terminals/~messages docks used to disappear when there was nothing to show, but that behavior was lost when they were replaced by the official plugins mounted as plain iframe docks. Restored server-side: each plugin's dock now sets its when clause to 'false' while its session/message collection is empty (and clears it otherwise), reacting live to terminal/message events.

Linked Issues

Additional context

• The inspector dock id is pinned via a shared DEVTOOLS_INSPECTOR_DOCK_ID constant so the node side (mount) and client (visibility gate) agree.
• Added unit tests covering the inspector default-hidden / opt-in / management-view cases, and refreshed the kit constants API snapshot for the new export.
• Verified with pnpm lint, pnpm typecheck, pnpm test (191 passing), and pnpm build.

This PR was created with the help of an agent.

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commit: dbd2d48