fix(lsp): fix bun-based LSP server auto-installation

[AHaldner]

Summary

Fixes auto-installation of bun-based LSP servers (Svelte, Astro, Vue, Pyright, etc.) that were failing silently.

Issues

1. Using bun install <pkg> instead of bun add <pkg> - install doesn't add new packages
2. Using stdout: "pipe" without reading output caused buffer deadlock
3. Missing package.json in ~/.local/share/opencode/bin/ caused bun to walk up and use a parent package.json

Changes

• Change bun install → bun add for all 8 LSP installers
• Change stdout/stderr/stdin: "pipe" → "ignore" to prevent deadlock
• Create empty package.json in bin directory on startup to anchor bun installs