Add structured issue template and coding standards to enforce machine-readable tasks.

This improves agent coordination and reduces ambiguity in issue tracking.

- `.gitea/ISSUE_TEMPLATE/agent_task.md` provides a standard form
- `scripts/create_structured_issue.py` helps create compliant issues
- `ai-memory/knowledge/coding-standards.md` documents the requirement

Fixes #?? (part of broader agent quality initiative)