fix(ci): sync tweet and README after all release artifacts are published (#3531)

The tweet was firing on `release: published` immediately when the GitHub
Release was created, but Docker push, crates.io publish, and website
redeploy were still in-flight. This meant users saw the tweet before
they could actually pull the new Docker image or install from crates.io.

Convert tweet-release.yml and sync-readme.yml to reusable workflows
(workflow_call) and call them as the final jobs in both release
pipelines, gated on completion of docker, crates-io, and
redeploy-website jobs.

Before: gh release create → tweet fires immediately (race condition)
After:  gh release create → docker + crates + website → tweet + readme

.github/workflows/sync-readme.yml

@@ -1,8 +1,11 @@
 name: Sync README
 
 on:
-  release:
-    types: [published]
+  # Called by release workflows AFTER all publish steps complete.
+  workflow_call:
+    secrets:
+      RELEASE_TOKEN:
+        required: true
   workflow_dispatch:
 
 permissions: