Add plugin marketplace configuration

Create comprehensive workflow-based plugin marketplace with 20 plugins:

Workflow-Based Plugins (12):
- full-stack-development: Complete feature implementation
- security-hardening: Threat modeling and vulnerability assessment
- data-ml-pipeline: End-to-end ML/AI with MLOps
- incident-response: Production debugging and hotfix deployment
- performance-optimization: System-wide profiling and optimization
- tdd-development: Test-driven development cycles
- code-quality-review: Multi-perspective code analysis
- git-automation: Version control workflow automation
- legacy-modernization: Codebase migration and refactoring
- multi-platform-apps: Cross-platform development coordination
- cicd-automation: CI/CD pipeline orchestration
- agent-optimization: AI agent improvement and prompt engineering

Specialist Plugins (8):
- documentation-generation: API docs, diagrams, technical writing
- cloud-infrastructure: AWS/Azure/GCP, Kubernetes, Terraform
- database-operations: Architecture, optimization, administration
- language-specialists: 15 programming language experts
- seo-content-suite: 10 SEO optimization specialists
- business-operations: Business, HR, legal, support, sales
- specialized-domains: Blockchain, fintech, payments, gaming
- research-utilities: Research, DX optimization, context management

Each workflow plugin bundles:
- Workflow orchestrator commands
- All required agents for the workflow
- Supporting tools and utilities

Marketplace Configuration:
- .claude-plugin/marketplace.json with 20 comprehensive plugins
- strict: false for all plugins (marketplace entry serves as manifest)
- Proper path references to agents/, workflows/, and tools/ directories
- Update README with plugin marketplace installation instructions

Available October 9, 2025 via /plugin marketplace add wshobson/agents

README.md

@@ -17,6 +17,31 @@ This unified repository provides everything needed for intelligent automation an
 
 ## Installation
 
+### Plugin Marketplace (Recommended - Available October 9, 2025)
+
+Install workflow-based plugin collections directly from the Claude Code plugin marketplace:
+
+```bash
+# Add the marketplace
+/plugin marketplace add wshobson/agents
+
+# Browse available plugins
+/plugin list
+
+# Install workflow-based plugins
+/plugin install full-stack-development
+/plugin install security-hardening
+/plugin install data-ml-pipeline
+/plugin install incident-response
+
+# Install infrastructure/specialist plugins
+/plugin install cloud-infrastructure
+/plugin install language-specialists
+/plugin install seo-content-suite
+```
+
+### Manual Installation
+
 ```bash
 cd ~/.claude
 git clone https://github.com/wshobson/agents.git