Establish org-owned accounts for project communications (Slack, Discord, social)

## Why
Most third-party SaaS the project relies on — chat platforms, social handles, analytics, status pages — binds accounts to an email and an individual. As long as those sit under a personal email (a maintainer's `@gmail.com`), the project is one ownership-transfer headache (or one person leaving) away from losing a community channel or brand handle.

This issue tracks creating dedicated, org-owned accounts for every such service so identity rotates with the org, not the individual.

## Action
- [ ] Provision a shared maintainers inbox (e.g. `maintainers@`) as the registration email for all third-party accounts — depends on [[Register and own a domain for Fallout]]
- [ ] Slack — create a Fallout workspace (or migrate the existing one) under the maintainers inbox; document admin handover
- [ ] Discord — server owned by the org account, not a personal handle
- [ ] Social handles — register/transfer X/Twitter, Bluesky, Mastodon (fosstodon.org or similar) so brand names are reserved even if unused
- [ ] LinkedIn — a project/company page so contributors can list it
- [ ] Analytics / error-tracking / status-page accounts (Plausible, Sentry, Statuspage) — under the org inbox
- [ ] Document each account in a maintainer-only store: handle, registration email, admins, recovery method
- [ ] Process for adding/removing admins as maintainers join or leave

## Coordinate with
- [[Create Fallout GitHub organization and transfer repositories]] — org name should match social handles where possible
- [[Register and own a domain for Fallout]] — required for the shared inbox
- [[Establish nuget.org organization account for Fallout.* packages]] — same registration-email pattern

## Done when
- A shared maintainers inbox exists on the project domain and is the registration email for every account above
- Every account is owned by the org or shared inbox — no personal handles in the chain of custody
- An up-to-date inventory (handle, email, admins, recovery) is maintained somewhere only maintainers can read