docs: add @openchamber/opencode-claude to plugins

data/plugins/opencode-claude.yaml

@@ -0,0 +1,9 @@
+name: "@openchamber/opencode-claude"
+repo: https://github.com/openchamber/opencode-claude
+npm: "@openchamber/opencode-claude"
+tagline: Claude Code in OpenCode — local CLI auth, Agent SDK harness, effort variants, tools/MCP, images & compact.
+description: Anthropic provider plugin for OpenCode
+kind: plugin
+topics:
+  - providers
+compat: v2