docs: add recovery guide and link it from README, quickstart, and troubleshooting (#1283)

Add a consolidated Recovery page that answers "what do I do if Sencho
breaks?" in one place. It covers getting back to a working state when
Sencho itself fails, a stack deploy fails, an admin is locked out of
sign-in, Docker is unavailable, or a remote node is unreachable, and
summarizes each path with a link to the authoritative detail page rather
than duplicating it.

The page opens by stating the core safety fact: Sencho keeps its state in
DATA_DIR and COMPOSE_DIR and treats compose files on disk as the source of
truth, so recovery is mostly file-level and running containers are
unaffected by a Sencho outage. It points to Backup & Restore as the
prerequisite.

Link the guide from the README documentation section, the quickstart
"where to next" cards, and the top of the troubleshooting page.

README.md

@@ -186,6 +186,7 @@ Sencho does not emit telemetry, analytics, or crash reports. The only outbound t
 ## Documentation, community, and license
 
 - **Documentation:** [docs.sencho.io](https://docs.sencho.io)
+- **If something breaks:** the [Recovery guide](https://docs.sencho.io/operations/recovery) covers getting back to a working state when Sencho, a deploy, sign-in, Docker, or a node fails.
 - **Community:** [GitHub Discussions](https://github.com/studio-saelix/sencho/discussions)
 - **Contributing:** [CONTRIBUTING.md](CONTRIBUTING.md)
 - **Security:** [SECURITY.md](SECURITY.md). Do not open public issues for security vulnerabilities.