MCP library validates schema BEFORE call_tool handler runs, so
our _coerce_types function never gets a chance to convert strings.
Changed all integer fields to accept both types:
- issue_number, milestone_id, pr_number, depends_on, milestone, limit, position
This fixes: "Input validation error: '312' is not of type 'integer'"
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>