chore(github): add bug, feature and chore issue templates

Adds the three issue templates plus config.yml, which disables blank
issues and routes security reports to the private policy. Supports the
issue-first contribution flow.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Enes Yağız

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,27 @@
+---
+name: Bug report
+about: A package whose release notes are wrong or missing, or anything else that misbehaves
+title: 'bug: '
+labels: bug
+---
+
+<!-- Security problems do NOT go here — use SECURITY.md. -->
+
+## What happened
+
+<!-- What you saw, and what you expected instead. -->
+
+## Where
+
+- Registry: <!-- nuget / npm / pypi / pub.dev / maven / packagist -->
+- Package:
+- Versions compared: <!-- from -> to -->
+- URL (if any):
+
+## Steps to reproduce
+
+1.
+
+## Notes
+
+<!-- Logs, screenshots, anything else. A pull request that fixes this should link it with "Closes #". -->

.github/ISSUE_TEMPLATE/chore.md

@@ -0,0 +1,20 @@
+---
+name: Chore
+about: Maintenance, tooling, CI, dependencies, docs or process — no user-facing behaviour change
+title: 'chore: '
+labels: chore
+---
+
+## What
+
+<!-- The maintenance task: what changes and where. -->
+
+## Why
+
+<!-- Why it is worth doing now. -->
+
+## Done when
+
+- [ ]
+
+<!-- A pull request for this chore links back with "Closes #". -->

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,5 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Security report
+    url: https://github.com/pkgdiff-dev/pkgdiff/security/policy
+    about: Report a security problem privately through SECURITY.md — never a public issue.

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,23 @@
+---
+name: Feature request
+about: A new capability or a larger change — agree the approach here before any code
+title: 'feat: '
+labels: enhancement
+---
+
+## Problem
+
+<!-- What is missing or painful today, and for whom. -->
+
+## Proposed approach
+
+<!-- How you would solve it. For a larger change, enough that we can agree on the approach before
+     a pull request is opened. -->
+
+## Alternatives considered
+
+<!-- Or "None". -->
+
+## Scope / out of scope
+
+<!-- What this does and does not cover. A pull request implementing it links back with "Closes #". -->