Provision a loopover-owned Posthog project for the hosted fleet

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Problem

Split from #4934. Error tracking/tracing (src/selfhost/sentry.ts) only activates if an operator sets their own SENTRY_DSN — no centrally-owned Sentry project exists for the hosted fleet gittensory itself operates.

Proposal

Sign up for / configure a Posthog project owned by loopover itself (or confirm reuse of an existing org-level Posthog account if one already exists), and get everything setup.

Deliverables

• A real, loopover-owned Posthog project + project key.
• Project key stored as a control-plane secret (via Generalize src/orb/broker.ts into a multi-secret-type broker shared by ORB + AMS hosted #7174's generalized broker, not a plaintext env var), documented for Wire hosted control-plane + tenant containers to report to the central PostHog project (implements #4934) #7876 to consume.

Resources

• Wire hosted control-plane + tenant containers to report to the central PostHog project (implements #4934) #7876 (the repo-side wiring that consumes the project key once it exists)

Boundaries

Account/credential setup only — no application code. Real live account access a contributor structurally can't have.

maintainer-only — live third-party account/credential setup, not a GitHub-issue-shaped code change.

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Please note, this was originally planned for Sentry, however we have plans to migrate to Posthog due to it's much more generous free tier offerings and more extensive services/analytics coverage, which we've yet to implemented.

[linear-code]

JSO-5499