docs: Add task list size management guidance

[michael-wojcik]

Context

From PR #113 peer review (test engineer recommendation).

Description

Long-running projects could accumulate many tasks over time. The current documentation doesn't address task cleanup or archival strategies.

Suggested Content

• When to clean up completed tasks
• Archival strategies for historical tasks
• Impact of large task lists on performance
• Recommended task lifecycle management

Location

pact-plugin/reference/task-integration-guide.md - new section on task lifecycle management

Labels

documentation, enhancement