ci: matrix over Node 22 and 24, add the bench and packaging tiers (task 0040)

The workflow pinned Node 20, which reached end-of-life in April 2026, while
the manifest promised support down to it — so the entire claimed range below
the single tested version went unverified and its floor was unsupported.

Matrix over the two supported long-term-support majors and narrow the engine
range to `^22 || ^24`, naming exactly what is tested. Narrowing is free now
because nothing has been published and no tags exist.

The benchmark harness tier joins every leg: it is deterministic and needs no
network, and its non-default runner configuration made it easy to believe it
was running when it was not. The end-to-end and packaging tiers run on the
highest leg only, conditioned on a flag attached to that leg through a matrix
`include` entry rather than on a version number restated at each site. The
benchmark smoke tier stays out, since it would pass by skipping.

`@types/node` follows the new floor; it was the last Node 20 reference in the
manifest, and the typecheck runs on every leg.

package.json

@@ -5,7 +5,7 @@
   "type": "module",
   "license": "MIT",
   "engines": {
-    "node": ">=20"
+    "node": "^22 || ^24"
   },
   "bin": {
     "gitea-axi": "dist/main.js"
@@ -47,7 +47,7 @@
     "gitea-js": "^1.23.0"
   },
   "devDependencies": {
-    "@types/node": "^20.19.0",
+    "@types/node": "^22.20.1",
     "@vitest/coverage-v8": "^3.2.7",
     "tsx": "^4.23.1",
     "typescript": "^5.8.0",