Initial redis skill implementation

SKILL.md

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+---
+name: redis
+description: Redis in-memory cache with persistence and pub/sub
+metadata:
+  version: "1.0.0"
+  vibestack:
+    main: false
+    metrics-port: 9121
+---
+
+# Redis Skill
+
+Installs and configures [Redis](https://redis.io/) in-memory data store for caching, pub/sub messaging, and session storage.
+
+## Features
+
+- In-memory key-value store
+- RDB + AOF persistence
+- Pub/sub messaging
+- Optional authentication
+- Memory limit with eviction policy
+- Auto-registers with Caddy if domain set
+
+## Configuration
+
+### Environment Variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `REDIS_PORT` | `6379` | Redis port |
+| `REDIS_PASSWORD` | (none) | Optional authentication password |
+| `REDIS_MAXMEMORY` | `100mb` | Memory limit |
+| `REDIS_MAXMEMORY_POLICY` | `allkeys-lru` | Eviction policy when memory limit reached |
+| `REDIS_DATA_DIR` | `/data/redis` | Persistence directory |
+| `REDIS_APPENDONLY` | `yes` | Enable AOF persistence |
+| `REDIS_SAVE` | `900 1 300 10 60 10000` | RDB save intervals |
+| `REDIS_DOMAIN` | (none) | Domain for Caddy auto-config |
+
+### Output Variables
+
+After starting, the skill exports:
+
+| Variable | Example |
+|----------|---------|
+| `REDIS_URL` | `redis://:password@localhost:6379` |
+
+## Usage
+
+### As a dependency
+
+```yaml
+metadata:
+  vibestack:
+    requires:
+      - redis
+```
+
+### Connection
+
+```bash
+# Connect with redis-cli
+redis-cli -p 6379
+
+# With authentication
+redis-cli -p 6379 -a "$REDIS_PASSWORD"
+
+# From application
+REDIS_URL=redis://localhost:6379
+# or with auth
+REDIS_URL=redis://:password@localhost:6379
+```
+
+### Common Operations
+
+```bash
+# Set a key
+redis-cli SET mykey "Hello"
+
+# Get a key
+redis-cli GET mykey
+
+# Pub/sub
+redis-cli SUBSCRIBE mychannel
+redis-cli PUBLISH mychannel "Hello subscribers!"
+
+# Check memory usage
+redis-cli INFO memory
+```
+
+## Persistence
+
+Redis is configured with both RDB snapshots and AOF (Append Only File):
+
+- **RDB**: Point-in-time snapshots at configured intervals
+- **AOF**: Log of all write operations for durability
+
+Data is stored in `REDIS_DATA_DIR` (default: `/data/redis`).
+
+## Memory Management
+
+When `REDIS_MAXMEMORY` is reached, the `REDIS_MAXMEMORY_POLICY` determines behavior:
+
+| Policy | Description |
+|--------|-------------|
+| `allkeys-lru` | Evict least recently used keys (default) |
+| `volatile-lru` | Evict LRU keys with TTL set |
+| `allkeys-random` | Evict random keys |
+| `noeviction` | Return errors on write |
+
+## Caddy Integration
+
+If the `caddy` skill is present and `REDIS_DOMAIN` is set, Redis will be accessible via HTTPS (useful for Redis Insight or other GUI tools).
+
+## Security
+
+For production use:
+1. Always set `REDIS_PASSWORD`
+2. Restrict network access
+3. Use TLS for external connections