fix: use package export for @opentui/solid to support monorepos

[sandipwane]

Why

When running typecheck in a bun/npm workspace monorepo, it failed with:

error TS2307: Cannot find module '../node_modules/@opentui/solid/scripts/solid-plugin' 
or its corresponding type declarations.

Summary

• Changed ../node_modules/@opentui/solid/scripts/solid-plugin → @opentui/solid/bun-plugin
• Fixes module resolution in monorepo setups where dependencies are hoisted

Problem

The hardcoded relative path breaks when:

# Expected (single repo)
packages/opencode/node_modules/@opentui/solid/  ✓

# Actual (monorepo with hoisting)
packages/opencode/node_modules/@opentui/solid/  ✗ (doesn't exist)
node_modules/@opentui/solid/                     ✓ (hoisted here)

Solution

Use the proper package export which @opentui/solid already provides:

"exports": {
  "./bun-plugin": {
    "types": "./scripts/solid-plugin.d.ts",
    "import": "./scripts/solid-plugin.ts"
  }
}

Test Plan

• [x] Verified package exports ./bun-plugin
• [x] Tested in monorepo environment