feat: PM Agent plugin architecture with confidence check test suite

## Plugin Architecture (Token Efficiency)
- Plugin-based PM Agent (97% token reduction vs slash commands)
- Lazy loading: 50 tokens at install, 1,632 tokens on /pm invocation
- Skills framework: confidence_check skill for hallucination prevention

## Confidence Check Test Suite
- 8 test cases (4 categories × 2 cases each)
- Real data from agiletec commit history
- Precision/Recall evaluation (target: ≥0.9/≥0.85)
- Token overhead measurement (target: <150 tokens)

## Research & Analysis
- PM Agent ROI analysis: Claude 4.5 baseline vs self-improving agents
- Evidence-based decision framework
- Performance benchmarking methodology

## Files Changed
### Plugin Implementation
- .claude-plugin/plugin.json: Plugin manifest
- .claude-plugin/commands/pm.md: PM Agent command
- .claude-plugin/skills/confidence_check.py: Confidence assessment
- .claude-plugin/marketplace.json: Local marketplace config

### Test Suite
- .claude-plugin/tests/confidence_test_cases.json: 8 test cases
- .claude-plugin/tests/run_confidence_tests.py: Evaluation script
- .claude-plugin/tests/EXECUTION_PLAN.md: Next session guide
- .claude-plugin/tests/README.md: Test suite documentation

### Documentation
- TEST_PLUGIN.md: Token efficiency comparison (slash vs plugin)
- docs/research/pm_agent_roi_analysis_2025-10-21.md: ROI analysis

### Code Changes
- src/superclaude/pm_agent/confidence.py: Updated confidence checks
- src/superclaude/pm_agent/token_budget.py: Deleted (replaced by /context)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.claude-plugin/plugin.json

@@ -0,0 +1,20 @@
+{
+  "name": "pm-agent",
+  "version": "1.0.0",
+  "description": "Project Manager Agent with 90% confidence checks and zero-footprint memory",
+  "author": "SuperClaude Team",
+  "commands": [
+    {
+      "name": "pm",
+      "path": "commands/pm.md",
+      "description": "Activate PM Agent with confidence-driven workflow"
+    }
+  ],
+  "skills": [
+    {
+      "name": "confidence_check",
+      "path": "skills/confidence_check.py",
+      "description": "Pre-implementation confidence assessment (≥90% required)"
+    }
+  ]
+}