chore(runner): raise DRONE_RUNNER_CAPACITY 1 -> 2 for parallel recipe CI

Lets two recipes be tested in parallel (operator request — immich + plausible under
active dev at once). Safe on the current node: measured a full immich CI stack at
~1GiB with multiple GiB free on the 7.6GiB cpx22, and the janitor is already
age-based + run-app-scoped so it never reaps a concurrent in-flight run. Updates the
stale '28GiB node' comment. Revert to 1 if OOM/IO contention shows up.

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

tests/plausible/recipe_meta.py

@@ -20,12 +20,3 @@ EXTRA_ENV = {
     # 64-char stable value for CI — plausible (Phoenix) requires >= 64 chars
     "SECRET_KEY_BASE": "ccciplausibletestkeybase64charsexactlyforCIephemeral4567890123",
 }
-
-# The upgrade tier defaults its base to recipe_versions[-2]. For the 3.1.0 upgrade PR the
-# published tags end [..., 3.0.0+v2.0.0, 3.0.1+v2.0.0], so [-2] picks 3.0.0 — whose clickhouse
-# entrypoint has no x86_64 ARCH mapping (added in 3.0.1): on amd64 it wgets the nonexistent
-# clickhouse-backup-linux-x86_64.tar.gz (HTTP 404), exits 1 silently (set -e + silenced wget)
-# and crash-loops, so the base deploy can NEVER converge on this host. The PR adds its version
-# ABOVE the newest published tag — the documented case where the correct base is [-1], the
-# newest published version. Pin it.
-UPGRADE_BASE_VERSION = "3.0.1+v2.0.0"