refactor(opencode): keep plugin pty environment route local

[jlongster]

Summary

• keep PluginPtyEnvironment.layer as the explicit route-local PTY environment exception
• remove the redundant generic PTY environment provider from the embedded opencode HTTP routes

Testing

• bun typecheck
• bun test test/server/httpapi-v2-pty.test.ts
• bun turbo typecheck (pre-push)

Stack

1. refactor(opencode): build runtimes from layer nodes #34515 refactor(opencode): build runtimes from layer nodes
2. refactor(opencode): use layer nodes in remaining harnesses #34516 refactor(opencode): use layer nodes in remaining harnesses
3. refactor(opencode): remove app service layer exports #34517 refactor(opencode): remove app service layer exports
4. refactor(opencode): remove core service layer exports #34518 refactor(opencode): remove core service layer exports
5. refactor(opencode): keep plugin pty environment route local #34519 refactor(opencode): keep plugin pty environment route local

Previous: #34518
Base: remove-core-layers
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