docs: add cookbook/recipes documentation

[CybotTM]

Description

Users would benefit from a cookbook showing common patterns and best practices.

Missing Recipes

1. Basic Setup: Simple scheduler with logging
2. Retry Pattern: External API calls with retry
3. Circuit Breaker: Protecting failing services
4. Metrics Integration: Prometheus/StatsD examples
5. Graceful Shutdown: Kubernetes-style termination
6. Testing Jobs: Unit testing job functions
7. Dynamic Scheduling: Adding/removing jobs at runtime
8. Multi-Timezone: Handling jobs in different timezones

Example Recipe

# Recipe: Retry Pattern for External APIs

Problem: You need to call an external API that occasionally fails.

Solution:
\`\`\`go
c := cron.New(
    cron.WithChain(
        cron.Recover(logger),
        cron.RetryWithBackoff(logger, 3, time.Second, time.Minute, 2.0),
    ),
)

c.AddFunc("@every 5m", func() {
    resp, err := http.Get("https://api.example.com/data")
    if err != nil {
        panic(err)  // Will trigger retry
    }
    defer resp.Body.Close()
    // Process response...
})
\`\`\`

Key Points:
- Retry wraps the job, catching panics
- Exponential backoff prevents thundering herd
- Recover ensures scheduler continues if retries exhaust
\`\`\`

## Severity
🟢 **Low** - Documentation for adoption

## Found By
Pre-1.0 release code review with Zen/Gemini