ci: deploy over a pinned, single-purpose key instead of root

deploy-vps reached subquery1 as root, through appleboy/ssh-action referenced
by tag, with a key whose comment (mamostehp@MamostePC) made it look like a
person's. It now uses plain ssh with SUBQUERY_DEPLOY_KEY, which the host pins
(authorized_keys restrict,command=) to ops/host/subquery-deploy-ssh: the
commit SHA is its only input. subquery-deploy, run through sudo, does what
the workflow's script did, with three changes:

- It deploys exactly the SHA CI was triggered for, and only a commit on main.
- The host's local edits to tracked files (the indexer manifests) are put
  back whether the deploy succeeds or fails. Before, a failed build exited
  before `stash pop` and left them stashed.
- Only tracked files are stashed. Stashing untracked ones too (.yarn/, which
  yarn install recreates) made every pop fail half-way; that is how 13 stash
  entries piled up on the host.

test-deploy.sh covers this against a scratch clone (red with the restore
trap removed); CI runs it with shellcheck. subquery1's host key is pinned.
The indexer endpoints themselves are unchanged. Actions pinned to SHAs; the
secret scanner's own AGPL licence is allowed in dependency review.

.github/workflows/auto-pr.yml

@@ -12,7 +12,7 @@ jobs:
       pull-requests: write
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4.4.0
 
       - name: Create or update PR
         env: