Bump opencode 1.14.41 -> 1.14.42

opencode-ai 1.14.42 was released; bump OPENCODE_VERSION default in
Dockerfile and Dockerfile.variant. Container changes accumulated since
v1.14.41b ride along with this tagged release: pi package rename to
@earendil-works/*, npm-prefix-on-volume fix, smoke-test query fix, Hub
doc rewrite, README/AGENTS docs catchup.

CHANGELOG promoted: Unreleased -> v1.14.42 (2026-05-09). The
split-base build pipeline note stays under a fresh Unreleased \u2014 it's
merged to main but not yet validated end-to-end via dispatch test, so
it does not ship with v1.14.42 (the production docker-publish.yml on
tag push is still authoritative).

Release contents:
- Bump: opencode 1.14.41 -> 1.14.42
- Rename: @mariozechner/pi-coding-agent -> @earendil-works/pi-coding-agent
- Fix: NPM_CONFIG_PREFIX on volume so 'pi install npm:<pkg>' as
  developer survives container recreate AND image rebuild
- Fix: smoke-test queries /usr prefix for npm ls -g check
- Docs: Hub doc rewrite (24997 -> 5529 bytes), README pi section
  catchup (6 -> 7 extensions, mcp-loader documented), AGENTS
  release-day checklist updates

Dockerfile.variant

@@ -32,7 +32,7 @@ ARG USER_NAME=developer
 
 # ── Install opencode via npm ─────────────────────────────────────────
 ARG INSTALL_OPENCODE=true
-ARG OPENCODE_VERSION=1.14.41
+ARG OPENCODE_VERSION=1.14.42
 RUN if [ "${INSTALL_OPENCODE}" = "true" ]; then \
       NPM_CONFIG_PREFIX=/usr npm install -g opencode-ai@${OPENCODE_VERSION} && \
       opencode --version ; \