chore(ci): bump ci-base image node 22 -> 24-alpine

Follow-up to the CI cache work (#635/#637), sequenced separately so the
runtime-version change carries zero cache variables. node:24 is Active
LTS; node:26 is held until it reaches LTS (Oct 2026) since the Current
line risks node-gyp native-module breakage (better-sqlite3, canvas,
sharp, node-pty compile from source on the musl runner).

Only Dockerfile.ci's base changes; ci.yml/publish.yml comments updated
for accuracy. The ci-base image rebuilds automatically on merge (the
Dockerfile.ci path filter in ci-image.yml).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.woodpecker/ci.yml

@@ -1,5 +1,5 @@
 # &node_image is the pre-baked CI base built by .woodpecker/ci-image.yml:
-# node:22-alpine + python3/make/g++/postgresql-client + pnpm + a warm pnpm
+# node:24-alpine + python3/make/g++/postgresql-client + pnpm + a warm pnpm
 # store. The install step resolves from the baked store (--prefer-offline)
 # instead of paying a ~731s cold fetch + native compile every run.
 variables: