feat(opencode): add native v2 plugin entrypoint

[peeyush-ciridae]

Summary

• add a native OpenCode v2 plugin entrypoint at @dataforxyz/agent-intercom-opencode/v2
• bridge the existing Intercom runtime onto the v2 plugin, tool, session, and event APIs
• filter the global v2 event stream by project location so messages cannot be routed across unrelated panes
• preserve the existing v1 entrypoint and behavior
• document the v2 configuration and include the new bundle in published packages

Validation

• npm run typecheck
• full test suite: 144 tests passed
• production bundle build
• package dry run confirmed dist/plugin-v2.mjs is published