Add production deployment docs

[nscuro]

Also refines scaling docs, and adds backup and upgrading guides. These will likely need refinement as users try to make sense of them, but it's a starting point, and better what we had previously (i.e. nothing).

[Copilot]

Pull request overview

Adds an initial set of production-oriented administration documentation and updates existing docs to link into the new operational guidance (production deployment baseline, scaling refinements, backup/restore, and rolling upgrades), plus a new architecture “deployment topology” concept page.

Changes:

• Introduces new administration guides: Deploying to production, Backing up and restoring, and Upgrading running instances.
• Refactors the Scaling guide to focus on web/worker separation, throughput levers, connection pooling, vertical scaling, and isolating the engine database.
• Adds an architecture Deployment topology page and updates navigation/quickstart “What’s next” links to surface the new guidance.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
docs/tutorials/quickstart.md	Updates “What’s next” links to point to production deployment guidance and other next steps.
docs/reference/configuration/dex-engine.md	Updates scaling deep-link to the new/renamed scaling section anchor.
docs/reference/configuration/application.md	Documents default JVM flags and how to extend them via EXTRA_JAVA_OPTIONS.
docs/guides/administration/deploying-to-production.md	New baseline production deployment guide (sizing, HA, TLS, observability, backup/upgrade planning).
docs/guides/administration/scaling.md	Reworks scaling guidance around workload separation, throughput tuning, pooling, vertical scaling, and engine DB isolation.
docs/guides/administration/backing-up.md	New backup/restore guidance including engine DB considerations and post-restore behavior.
docs/guides/administration/upgrading-instances.md	New rolling-upgrade guidance for multi-instance clusters, including web/worker split considerations.
docs/guides/administration/.pages	Adds new guides to the Administration navigation in a more logical order.
docs/concepts/architecture/index.md	Adds a topology section linking to the new deployment topology page.
docs/concepts/architecture/deployment.md	New deployment topology/coordination/recovery conceptual documentation (with diagram).
docs/concepts/architecture/.pages	Adds the new deployment topology page to the Architecture navigation.

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