docs: add community Railway self-hosting option

[Lukem121]

Summary

• Adds a Railway self-hosting path to the README with a Deploy on Railway button pointing at the community template: https://railway.com/deploy/openseo
• Adds docs/SELF_HOSTING_RAILWAY.md covering the GHCR image + /app/.wrangler volume, DataForSEO key, local_noauth security note, and Image Auto Updates
• Clearly labels the template as a community listing (not an official every-app product)
• Deploy links use clean URLs with no UTM/tracking parameters

Context

OpenSEO already ships a Docker self-host path (ghcr.io/every-app/open-seo). This template wraps that same image on Railway so people can one-click deploy with persistence. Happy to adjust wording/placement if you'd rather keep Railway out of the main README or link only from Discord.

Test plan

• README Self-Hosting section renders the button and links correctly
• docs/SELF_HOSTING_RAILWAY.md links resolve
• Deploy button opens https://railway.com/deploy/openseo with no query params

[sorcerai]

Current head fails the repository gate on exact main+#153: pnpm ci:check reports a Prettier violation in README.md. Please format the README change and rerun ci:check; the Railway documentation content and security warning otherwise look safe.

[Lukem121]

Rebased onto latest main and fixed the Prettier formatting in README.md. I re-ran pnpm ci:check and it passes.

[bensenescu]

Closing because this is default not secure since Railway doesn't have a "Cloudflare Access" type feature. I'm working on a better way to deploy to services like Railway securely, just may be a few weeks.

[Lukem121]

Updated the community template so it's password-gated by default (Gate service + SITE_PASSWORD in front of OpenSEO). Docs in this PR match that. Reopened for another look.