Add issue templates and disable blank issues

Four templates: bug report (with environment table and platform-vs-plugin
gate), feature request (with problem statement and core-appropriateness
question), IDE/platform support request, and a config that disables
blank issues and redirects questions to Discord.

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,34 @@
+---
+name: Feature Request
+about: Propose a change or addition to Superpowers
+labels: enhancement
+---
+
+<!--
+BEFORE FILING: Search open AND closed issues. Many features have been
+requested before — some were implemented differently, some are in
+progress, and some were intentionally declined.
+-->
+
+- [ ] I searched existing issues and this has not been proposed before
+
+## What problem does this solve?
+<!-- Describe the problem from your own experience. What were you doing,
+     what went wrong or was missing, and why did it matter?
+
+     "It would be cool if..." is not a problem statement. -->
+
+## Proposed solution
+<!-- What specifically do you want to happen? Be concrete. -->
+
+## What alternatives did you consider?
+<!-- What other approaches could solve the same problem? Why is your
+     proposal better? -->
+
+## Is this appropriate for core Superpowers?
+<!-- Would this benefit someone working on a completely different kind
+     of project? If this is specific to your domain, workflow, or a
+     third-party tool, it may belong as its own plugin instead. -->
+
+## Context
+<!-- Optional: version info, harness, model, workflow where you hit this. -->