Add issue templates for bugs and feature requests

[Marvell69]

Without issue templates, bug reports lack the information needed to reproduce issues quickly. Templates guide reporters to include browser, wallet, and reproduction steps.

Requirements and context

• Create .github/ISSUE_TEMPLATE/bug_report.md: steps to reproduce, expected behaviour, actual behaviour, browser, wallet (Freighter/WalletConnect), wallet version, Stellar network (testnet/mainnet), screenshot/console log
• Create .github/ISSUE_TEMPLATE/feature_request.md: user story, proposed UI/UX, alternatives considered, impact on existing flows
• Create .github/ISSUE_TEMPLATE/design_feedback.md: component name, screenshot, specific feedback

Suggested execution

git checkout -b chore/issue-templates

• Create all three issue templates
• Test by opening a test issue

Example commit message
chore: add bug, feature request, and design feedback issue templates