[BUG] `apm install -g --target opencode` installs skills to `~/.opencode/` instead of `~/.config/opencode/`

[tr4l]

Describe the bug

When running apm install -g --target opencode, skills are silently deployed to ~/.opencode/skills/<skill>/ instead of the correct user-scope path ~/.config/opencode/skills/<skill>/. No error or warning is raised.

This is caused by two related issues in skill_integrator.py:

1. Wrong root dir used — _integrate_native_skill (line 717) uses target.root_dir (.opencode) directly instead of calling target.effective_root(user_scope=True) (.config/opencode). The user_scope flag is never propagated into the skill integrator.
2. auto_create guard missing — All other integrators (agent, command, instruction, prompt) skip deployment when target.auto_create=False and the target dir doesn't already exist. skill_integrator.py has no such guard, so it unconditionally creates ~/.opencode/skills/ from scratch via mkdir(parents=True).

To Reproduce

1. apm install -g --target opencode <some-skill-package>
2. Observe ~/.opencode/skills/<skill>/ is created
3. ~/.config/opencode/skills/ is never touched

Expected behavior

Skill installed to ~/.config/opencode/skills/<skill>/. If ~/.config/opencode/ doesn't exist and auto_create=False, skip with a warning (consistent with other integrators).

Relevant code

• src/apm_cli/integration/skill_integrator.py:717 — target.root_dir should be target.effective_root(user_scope=<flag>)
• src/apm_cli/integration/skill_integrator.py:728 — mkdir called unconditionally, no auto_create guard
• src/apm_cli/integration/targets.py:99-107 — effective_root() exists and handles this correctly, just not called
• Compare with agent_integrator.py:115, command_integrator.py:135 for the correct auto_create pattern

Environment

• OS: WSL (Linux)
• Python Version: 3.12.3
• APM Version: 0.8.9

Logs

No error output — failure is silent.