Add default issue forms and repository override guidance

[Scriptception]

Problem

Most repositories expose only generic default labels and no organization-wide issue forms, producing inconsistent problem statements and missing validation context.

User outcome

Users can submit actionable defects and feature outcomes while maintainers can tailor forms where a product needs different evidence.

Scope

• Add default defect and feature-request forms using existing default labels.
• Request environment, observed and expected behavior, reproduction, impact, user outcome, scope, and validation as appropriate.
• Add issue configuration links for support and sensitive disclosure.
• Document how a repository overrides, extends, or disables inherited forms.

Non-goals

• Creating forms for every product domain.
• Requesting secrets, customer data, or sensitive logs.

Acceptance criteria

• Repositories without local forms offer useful defect and feature paths.
• Forms apply only label names that exist by default.
• Sensitive-report and support links route away from ordinary issues.
• Override behavior is tested and documented.

Validation

• Preview rendered forms in a test repository or branch.
• Submit dry-run examples for a defect and a feature outcome and assess completeness.

Relationships

• Depends on default support and disclosure guidance.
• Complements contribution and pull-request defaults.