[BUG] OpenCode MCP adapter rejects documented global user configuration

Describe the bug

APM rejects an explicit global MCP installation for OpenCode even when the user's documented global OpenCode configuration already exists.

To Reproduce

Run:

$ apm install -g --target opencode \
    --mcp example --transport http --url https://example.com/mcp

Error: Selected targets are unavailable for user-scope MCP installation
(opencode; source: --target flag); choose a global-capable --target or omit --global

No OpenCode configuration is changed.

Expected behavior

apm install -g --target opencode should support MCP deployment to OpenCode's documented global configuration and preserve unrelated existing settings.

Project-scoped OpenCode installation should continue to use project opencode.json independently.

Environment (please complete the following information):

• OS: macOS
• Python Version: 3.14.7
• APM Version: 0.31.0 installed with Homebrew
• VSCode Version (if relevant): Not applicable

Logs

The complete relevant error is included in the reproduction above.

Additional context

APM's OpenCode adapter explicitly disables user scope, selects project-root opencode.json, and requires a project .opencode/ directory. The global MCP installer then rejects adapters without user-scope support.

OpenCode documents a supported user-level configuration model:

• Its global configuration is ~/.config/opencode/opencode.json and applies user-wide.
• Its configuration locations are merged, preserving non-conflicting settings from each source.
• MCP servers are declared under the top-level mcp key.
• A remote MCP entry uses type: "remote", url, and optional fields such as enabled and headers.

Start with src/apm_cli/adapters/client/opencode.py around lines 37-69 and src/apm_cli/integration/mcp_integrator_install.py around lines 570-600 to trace how target scope and the global-install rejection are determined. Reproduce the documented command, then verify that global OpenCode configuration is supported, unrelated settings are preserved, and project-scoped installation remains independent.