feat(opencode): implement connection, server management, and HTTP API client

refactor(opencode): address code review issues for Task 1

feat(opencode): implement server control and HTTP request APIs

refactor(opencode): address code review issues for Task 2

feat(opencode): implement SSE parsing, routing, and open stream APIs

refactor(opencode): address code review issues for Task 3

feat(opencode): implement major mode and streaming SSE content renderer

refactor(opencode): address code review issues for Task 4

feat(opencode): integrate customization group and mock tests for Task 4 review

feat(opencode): implement HTTP-mode routing for switch-to-buffer and send-command

Author: tninja