test: add automated test suite for opencode plugin

Create comprehensive tests in tests/opencode/ that verify the plugin
works correctly in an isolated test environment:

- setup.sh: Creates temp HOME and installs plugin with proper symlinks
- test-plugin-loading.sh: Verifies plugin structure and JavaScript syntax
- test-skills-core.sh: Unit tests for skills-core.js library functions
- test-tools.sh: Integration tests for use_skill/find_skills (requires OpenCode)
- test-priority.sh: Tests project > personal > superpowers priority
- run-tests.sh: Main test runner with options for integration tests

Run basic tests: ./tests/opencode/run-tests.sh
Run all tests: ./tests/opencode/run-tests.sh --integration

tests/opencode/setup.sh

@@ -0,0 +1,72 @@
+#!/usr/bin/env bash
+# Setup script for OpenCode plugin tests
+# Creates an isolated test environment with proper plugin installation
+set -euo pipefail
+
+# Get the repository root (two levels up from tests/opencode/)
+REPO_ROOT="$(cd "$(dirname "$0")/../.." && pwd)"
+
+# Create temp home directory for isolation
+export TEST_HOME=$(mktemp -d)
+export HOME="$TEST_HOME"
+export XDG_CONFIG_HOME="$TEST_HOME/.config"
+
+# Install plugin to test location
+mkdir -p "$HOME/.config/opencode/superpowers"
+cp -r "$REPO_ROOT/lib" "$HOME/.config/opencode/superpowers/"
+cp -r "$REPO_ROOT/skills" "$HOME/.config/opencode/superpowers/"
+
+# Copy plugin directory
+mkdir -p "$HOME/.config/opencode/superpowers/.opencode/plugin"
+cp "$REPO_ROOT/.opencode/plugin/superpowers.js" "$HOME/.config/opencode/superpowers/.opencode/plugin/"
+
+# Register plugin via symlink
+mkdir -p "$HOME/.config/opencode/plugin"
+ln -sf "$HOME/.config/opencode/superpowers/.opencode/plugin/superpowers.js" \
+       "$HOME/.config/opencode/plugin/superpowers.js"
+
+# Create test skills in different locations for testing
+
+# Personal test skill
+mkdir -p "$HOME/.config/opencode/skills/personal-test"
+cat > "$HOME/.config/opencode/skills/personal-test/SKILL.md" <<'EOF'
+---
+name: personal-test
+description: Test personal skill for verification
+---
+# Personal Test Skill
+
+This is a personal skill used for testing.
+
+PERSONAL_SKILL_MARKER_12345
+EOF
+
+# Create a project directory for project-level skill tests
+mkdir -p "$TEST_HOME/test-project/.opencode/skills/project-test"
+cat > "$TEST_HOME/test-project/.opencode/skills/project-test/SKILL.md" <<'EOF'
+---
+name: project-test
+description: Test project skill for verification
+---
+# Project Test Skill
+
+This is a project skill used for testing.
+
+PROJECT_SKILL_MARKER_67890
+EOF
+
+echo "Setup complete: $TEST_HOME"
+echo "Plugin installed to: $HOME/.config/opencode/superpowers/.opencode/plugin/superpowers.js"
+echo "Plugin registered at: $HOME/.config/opencode/plugin/superpowers.js"
+echo "Test project at: $TEST_HOME/test-project"
+
+# Helper function for cleanup (call from tests or trap)
+cleanup_test_env() {
+    if [ -n "${TEST_HOME:-}" ] && [ -d "$TEST_HOME" ]; then
+        rm -rf "$TEST_HOME"
+    fi
+}
+
+# Export for use in tests
+export -f cleanup_test_env
+export REPO_ROOT