community: add issue forms, pull request template, code of conduct, and CODEOWNERS

[teesofttech]

Why

GitHub community health is 57%. The repository has no issue templates, pull-request template, code of conduct, or CODEOWNERS. A large gateway backlog needs consistent reproduction details and ownership.

Scope

• Add bug, gateway request, security-sensitive report routing, and documentation issue forms.
• Add a PR template with tests, provider evidence, docs, security, and breaking-change checklist.
• Add CODE_OF_CONDUCT.md and CODEOWNERS.
• Add SECURITY.md with private vulnerability reporting instructions.
• Configure blank issue behavior appropriately.

Acceptance criteria

• New issues collect provider, environment, SDK version, sanitized logs, and reproduction details.
• Security reports are directed away from public issues.
• PRs prompt for test and documentation evidence.
• Owners are requested for gateway, core, docs, and workflow changes.
• Community profile reports all intended files.