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.

docs/operations/troubleshooting.mdx

@@ -7,6 +7,8 @@ description: Solutions to the most common Sencho setup and runtime problems.
   Sencho is currently in public beta on the path to v1.0. Core workflows are actively tested, but early users should review the [known limitations](https://github.com/studio-saelix/sencho/blob/main/KNOWN_LIMITATIONS.md) and avoid deploying it blindly on critical infrastructure without testing in their own environment first.
 </Note>
 
+If something has broken and you want a quick "what do I do now?" overview rather than a specific symptom, start with the [Recovery guide](/operations/recovery). It walks through getting back to a working state when Sencho, a deploy, sign-in, Docker, or a remote node fails, and links back here for the details.
+
 ## Containers won't start after deploy
 
 **Symptom:** You click Deploy and containers immediately exit or never appear.