#76 fix: align @next preview with OpenCode beta

Summary

• Align OpenTUI and Solid peers with OpenCode beta 0.0.0-beta-18027.
• Use the real @opencode-ai/plugin/tui Plugin.define and Context APIs.
• Include the plugin API as a runtime dependency for isolated npm installation.
• Add a prerelease changeset and update the lockfile.

Validation

• bun run typecheck
• bun test
• bun run check
• bun run build
• bun run test:package

Fixes the dependency-tree failure seen with: opencode2 plugin add oc-usage-limits-plugin@next

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Summary by cubic

Aligns the @next usage-limits plugin with the OpenCode beta TUI API so opencode2 plugin add oc-usage-limits-plugin@next installs cleanly. Old: local Plugin.define/custom context and a dev-only plugin dep. New: real @opencode-ai/plugin/tui Plugin.define/Context and a runtime @opencode-ai/plugin dep; peers match OpenTUI 0.5.7.

• Replaces local shims in src/index.ts and src/plugin.tsx with @opencode-ai/plugin/tui; updates tests to use Context.
• Adds runtime dependency @opencode-ai/plugin@0.0.0-beta-18027; bumps peers to @opentui/core@0.5.7, @opentui/solid@0.5.7, and solid-js@1.9.12; updates lockfile and adds a patch changeset.

Bolded rollout and migration details:

• Hosts must satisfy peer ranges: @opentui/core@0.5.7, @opentui/solid@0.5.7, solid-js@1.9.12.
• No plugin UI behavior change; only adoption of the official TUI API and dependency realignment.