feat!: require Node.js 22 — promise the runtime we actually test (#3825) (#3858)

Every published package declared engines.node ">=18.0.0". Node 18 reached
end-of-life on 2025-04-30 and Node 20 on 2026-04-30, so the compatibility
promise covered two runtimes nobody patches -- and, after #3830 moved CI to Node
22, two runtimes nothing in this repo verifies.

That left the promise and the evidence with no overlap at all:

  CI validates every PR on ......................... 22
  release.yml publishes from ....................... 22
  every shipped Docker image runs ................... 22
  engines.node promised users ...................... >=18

engines.node is now ">=22.0.0" across all 50 manifests -- the only runtime the
packages are built, tested and shipped on.

Node 24 (Active LTS since 2025-10-28) and Node 26 both satisfy the new range, so
anyone on 22+ is unaffected. npm/pnpm surface an unsatisfied engines as an
EBADENGINE warning rather than a hard failure, so existing installs on 18/20 do
not break the moment this lands -- but those runtimes are no longer tested, and
the failures are the kind that do not announce themselves (#3812: a native
dependency whose engines required a newer Node loaded anyway on the older one,
then killed the test worker at the process level with no JS error and a summary
that still said "passed").

The "Node 18+" prerequisite was restated in ten user-facing places (README,
CONTRIBUTING, the getting-started and deployment docs, the todo example, and the
objectstack-platform skill's compatibility field); all now say 22. A half-done
rename is worse than none. Changelogs and ADRs are historical records and were
left alone.

Shipped as a changesets `major`. The repo is in pre-release (rc) mode, where the
no-major guard stands aside by design -- accumulating breaking changes is what
the RC window is for -- so this does not block other PRs. Four other majors are
already pending in the same window.

Verified on Node 22: full build 71/71 and full test suite 129/129, both with
zero cache hits, 16921 tests declared and all 16921 accounted for.

Co-authored-by: Jack Zhuang <277994282+os-zhuang@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>

Author: os-zhuang

.changeset/engines-node-22.md

@@ -40,6 +40,6 @@
     "zod": "4.4.3"
   },
   "engines": {
-    "node": ">=18.0.0"
+    "node": ">=22.0.0"
   }
 }