Replace the Orbit dashboard with the new shell and Overview tab

What does this MR do and why?

Replaces the Orbit dashboard with a new shell, with the Overview, Schema, and Query editor tabs. The new Overview tab has a globe of your Orbit groups, an indexed-items card, alerts for an ended trial, a missing default group, and indexing, and a Quickstart panel with Ask GitLab Duo. There is no feature flag. The old Explore and Configuration tabs are deleted (about 6,000 lines): the 2D map, filter bar, table view, legend, the SaaS Configure button, and the Get Started section with the MCP endpoint and config modal, the one-click Use GitLab Orbit in GitLab Duo, and the suggested prompts. The Quickstart panel replaces Get Started. Events that only the old dashboard sent are marked as removed. Group.orbitTrial now resolves for up to 10 groups per request.

Closes gitlab-org/orbit/knowledge-graph#1361 (closed)

Related to gitlab-org/orbit/knowledge-graph#1368 (closed)

Screenshots or screen recordings

Before	After

Happy path	Indexing	Bad path	Disaster path

More recordings and screenshots

View	Recording or screenshot
Before
Quickstart closed
Indexing 1 of 2 groups
Trial ended
No Orbit default group
No GitLab Duo
Orbit off
Stats API down
Groups query down
Query editor
Schema
1024
390
390, graph
Dark

How to set up and validate locally

Go to /dashboard/orbit as an Owner of a group with Orbit on.

MR acceptance checklist

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