Remove legacy Markdown issue templates

[zeevdr]

Description

The issue template directory contains legacy Markdown templates (bug_report.md, feature_request.md) alongside the modern YAML form (bug_report.yml). GitHub renders the structured .yml forms, so the leftover .md files create a duplicate "Bug report" choice in the new-issue chooser and drift from the other repos. decree, decree-ui, and demos already use only the .yml forms plus config.yml.

Acceptance criteria

• bug_report.md removed (superseded by bug_report.yml)
• feature_request.md removed (rely on a repo feature_request.yml or the org-level template)
• New-issue chooser shows no duplicate templates
• Template layout consistent with decree / decree-ui / demos