fix: report OpenCode scrub package version

[rynfar]

Change

The published 0.2.2 package reports plugin version 0.1.0. Read the version from the shipped package.json so Release Please's package version and the runtime plugin metadata stay aligned. Add a regression assertion; prompt scrubbing behavior is unchanged.

Validation

• Baseline with the new assertion: 4 pass, 1 fail (0.1.0 reported versus package 0.2.2).
• npm ci, npm test (22 pass), npm run build, Node import of built plugin, and npm pack dry run passed.
• Real OpenCode 1.18.32 → LiteLLM 1.81.10 → isolated Meridian 1.76.3 → Claude Agent SDK / Opus 5.5 returned successfully. The plugin loaded as version 0.2.2; OpenCode fingerprint markers disappeared, and its client working directory remained. Local evidence artifact: opencode-scrub-live-YELnQO.
• The Nix package layout is being corrected in Meridian PR #1144 to preserve the metadata file imported at runtime.