Add ECA execute action for Summarization
### Problem/Motivation
The AI module's `Summarization` operation type has no corresponding ECA execute action in this module. ECA flows cannot drive `Summarization` without a custom action plugin.
Existing per-operation actions: Chat, Embedding, Moderation, Speech to Text, Text to Speech (`src/Plugin/Action/`).
### Proposed resolution
Add `Plugin\Action\Summarization` extending `AiConfigActionBase`, mirroring `Chat.php`:
- Plugin id: `ai_integration_eca_execute_summarization`
- Builds the matching Input class from `Drupal\ai\OperationType\Summarization\` and dispatches it through the configured provider.
- Add a `Kernel\Plugin\Action\SummarizationTest` mirroring the existing per-action tests.
### API changes
None.
---
_Filed with AI assistance (Claude Code)._
issue