Add lifecycle hooks automation skill (azd hooks best practices)

## Summary

There is no skill covering azd lifecycle hooks. This is a gap identified from an analysis of proposed azd skills (Azure/azure-dev#6501).

## Proposed Skill: hooks-automation

**Trigger scenarios:**
- Writing pre/post hooks for azd lifecycle events
- Debugging hook failures (PowerShell, bash, Python)
- Hook ordering and execution flow
- Common hook patterns (data seeding, config transforms, health checks)

**Coverage needed:**
- Hook types: preprovision, postprovision, predeploy, postdeploy, predown, postdown, prerestore, postrestore, prepackage, postpackage
- Hook configuration in azure.yaml (shell, run, continueOnError, interactive)
- Language-specific guidance: PowerShell, bash, Python
- Common patterns: database migrations, environment variable injection, API key rotation, smoke tests
- Error handling and debugging: \Continue, exit codes, stderr capture
- Windows vs Linux differences in hook execution

**Context:** PowerShell hook failures account for ~5% of all azd errors. The \zure-prepare\ skill mentions hooks in triggers but provides no guidance on writing, debugging, or managing them.

Start with the proposed hooks-automation skill scope and the azure.yaml hook configuration described in the issue, then review the referenced azd skills analysis in Azure/azure-dev#6501. Done means the skill covers the listed hook types, configuration options, language guidance, common patterns, error handling, debugging, and Windows/Linux differences.

Written by the indexing model from the issue text.