docs: add issue templates for bug reports and feature requests

[nearlyforget]

Description

This PR moves templates from ucp repository to org level to share across all repositories .
These templates ensure that contributors provide the necessary information (steps to reproduce, expected behavior, technical rationale) when filing bugs or proposing new features.

Key Changes

• Added .github/ISSUE_TEMPLATE/ folder containing:
  • Bug Report (.md and .yml forms): For standardized bug tracking.
  • Feature Request (.md and .yml forms): For new capability suggestions.
  • Enhancement Proposal (.md): For technical RFCs and protocol changes.

Category (Required)

• Infrastructure: CI/CD, Linters, or build scripts.
• Maintenance: Version bumps, lockfile updates, or minor bug fixes.

Related Issues

This is the foundational PR for establishing organization-wide health files and automation.

Checklist

• x] I have followed the [Contributing Guide (https://github.com/agentic-commerce/ucp/blob/main/CONTRIBUTING.md).
• I have updated the documentation (if applicable).
• My changes pass all local linting and formatting checks (verified via pre-commit).
• (For Core/Capability) I have included/updated the relevant JSON schemas.
• I have regenerated Python Pydantic models by running generate_models.sh under python_sdk.