deploy(althing): pin the post office to 3.6.3

Canonical intent still named the 3.6.2 digest while nh3-docker was running
3.6.3, so the next scripts/deploy-stack.sh run against this stack would have
silently rolled the fleet message bus back and taken the hyphenated-search
fix with it. Caught by forseti during independent post-deploy verification.

3.6.3 is the literal-search fallback: a query containing a hyphen was parsed
by FTS5 as a column filter, raised OperationalError, and search() returned []
— indistinguishable from "no results" — so every hyphenated term on this
fleet silently matched nothing. nh3-docker, irv-ml1, esh-docker-vm, tts-dev
and every other hyphenated name were unsearchable.

Deployed digest verified against the running container before this pin:
sha256:978f85533674ee248d6c6f29c54ffab0bc2cb16332c18c9fb8bfda1d566e2de4,
built from git archive of tag v3.6.3 (5de41b7). The image line is the only
difference between canonical and live; the two files are now identical, so a
managed deploy is a no-op rather than a regression.

stacks/althing-post-office/compose.yaml

@@ -51,7 +51,7 @@ services:
     # Digest-pinned, not tag-floating: `:3.0.0` is a mutable pointer on a registry
     # anyone can re-push, and this container is the fleet's whole message bus. The
     # tag is kept alongside the digest purely so a human can read what it is.
-    image: gitea.phasefinal.com/claude-bot/althing-post-office:3.6.2@sha256:9bf9808eb54ed828ac1ae2e18a2021d9ffcca60bf25dc8a51b4fc5a2b2960c77
+    image: gitea.phasefinal.com/claude-bot/althing-post-office:3.6.3@sha256:978f85533674ee248d6c6f29c54ffab0bc2cb16332c18c9fb8bfda1d566e2de4
     container_name: althing-post-office
 
     # ─── Host networking, so the bind guard keeps working ────────────