Move blockchain app READMEs to centralized documentation

- Relocate blockchain-event-bridge README content to docs/apps/blockchain/blockchain-event-bridge.md
- Relocate blockchain-explorer README content to docs/apps/blockchain/blockchain-explorer.md
- Replace app READMEs with redirect notices pointing to new documentation location
- Consolidate documentation in central docs/ directory for better organization

docs/apps/plugins/plugin-registry.md

@@ -0,0 +1,217 @@
+# Plugin Registry
+
+## Status
+✅ Operational
+
+## Overview
+Registry plugin for managing plugin metadata, versions, and availability in the AITBC ecosystem.
+
+## Architecture
+
+### Core Components
+- **Registry Database**: Stores plugin metadata and versions
+- **Metadata Manager**: Manages plugin metadata
+- **Version Controller**: Controls plugin versioning
+- **Availability Checker**: Checks plugin availability
+- **Indexer**: Indexes plugins for search
+
+## Quick Start (End Users)
+
+### Prerequisites
+- Python 3.13+
+- PostgreSQL database
+- Storage for plugin files
+
+### Installation
+```bash
+cd /opt/aitbc/apps/plugin-registry
+.venv/bin/pip install -r requirements.txt
+```
+
+### Configuration
+Set environment variables in `.env`:
+```bash
+DATABASE_URL=postgresql://user:pass@localhost/plugin_registry
+STORAGE_PATH=/opt/aitbc/plugins/storage
+INDEXING_ENABLED=true
+```
+
+### Running the Service
+```bash
+.venv/bin/python main.py
+```
+
+## Developer Guide
+
+### Development Setup
+1. Clone the repository
+2. Create virtual environment: `python -m venv .venv`
+3. Install dependencies: `pip install -r requirements.txt`
+4. Set up database
+5. Configure storage path
+6. Run tests: `pytest tests/`
+
+### Project Structure
+```
+plugin-registry/
+├── src/
+│   ├── registry_database/    # Registry database
+│   ├── metadata_manager/    # Metadata management
+│   ├── version_controller/   # Version control
+│   ├── availability_checker/ # Availability checking
+│   └── indexer/             # Plugin indexing
+├── storage/                 # Plugin storage
+├── tests/                   # Test suite
+└── pyproject.toml           # Project configuration
+```
+
+### Testing
+```bash
+# Run all tests
+pytest tests/
+
+# Run registry database tests
+pytest tests/test_registry.py
+
+# Run indexer tests
+pytest tests/test_indexer.py
+```
+
+## API Reference
+
+### Plugin Registration
+
+#### Register Plugin
+```http
+POST /api/v1/registry/plugins
+Content-Type: application/json
+
+{
+  "plugin_id": "string",
+  "name": "string",
+  "version": "1.0.0",
+  "description": "string",
+  "author": "string",
+  "category": "string",
+  "metadata": {}
+}
+```
+
+#### Update Plugin Metadata
+```http
+PUT /api/v1/registry/plugins/{plugin_id}
+Content-Type: application/json
+
+{
+  "version": "1.0.1",
+  "description": "updated description",
+  "metadata": {}
+}
+```
+
+#### Get Plugin Metadata
+```http
+GET /api/v1/registry/plugins/{plugin_id}
+```
+
+### Version Management
+
+#### Add Version
+```http
+POST /api/v1/registry/plugins/{plugin_id}/versions
+Content-Type: application/json
+
+{
+  "version": "1.1.0",
+  "changes": ["fix1", "feature2"],
+  "compatibility": {}
+}
+```
+
+#### List Versions
+```http
+GET /api/v1/registry/plugins/{plugin_id}/versions
+```
+
+#### Get Latest Version
+```http
+GET /api/v1/registry/plugins/{plugin_id}/latest
+```
+
+### Availability
+
+#### Check Availability
+```http
+GET /api/v1/registry/plugins/{plugin_id}/availability?version=1.0.0
+```
+
+#### Update Availability
+```http
+POST /api/v1/registry/plugins/{plugin_id}/availability
+Content-Type: application/json
+
+{
+  "version": "1.0.0",
+  "available": true,
+  "download_url": "string"
+}
+```
+
+### Search
+
+#### Search Plugins
+```http
+POST /api/v1/registry/search
+Content-Type: application/json
+
+{
+  "query": "analytics",
+  "filters": {
+    "category": "string",
+    "author": "string",
+    "version": "string"
+  },
+  "limit": 20
+}
+```
+
+#### Reindex Plugins
+```http
+POST /api/v1/registry/reindex
+```
+
+## Configuration
+
+### Environment Variables
+- `DATABASE_URL`: PostgreSQL connection string
+- `STORAGE_PATH`: Path for plugin storage
+- `INDEXING_ENABLED`: Enable plugin indexing
+- `MAX_METADATA_SIZE`: Maximum metadata size
+
+### Registry Parameters
+- **Plugin ID Format**: Format for plugin identifiers
+- **Version Schema**: Version numbering scheme
+- **Metadata Schema**: Metadata validation schema
+
+### Indexing
+- **Full Text Search**: Enable full text search
+- **Faceted Search**: Enable faceted search
+- **Index Refresh Interval**: Index refresh frequency
+
+## Troubleshooting
+
+**Plugin registration failed**: Validate plugin metadata and version format.
+
+**Version conflict**: Check existing versions and compatibility rules.
+
+**Index not updating**: Verify indexing configuration and database connectivity.
+
+**Storage full**: Review storage usage and cleanup old versions.
+
+## Security Notes
+
+- Validate plugin metadata on registration
+- Implement access controls for registry operations
+- Scan plugins for security issues
+- Regularly audit registry entries
+- Implement rate limiting for API endpoints