fix(gh): move issue template to ISSUE_TEMPLATE/ dir

[agilgur5]

Summary

Fix the issue template not working by moving it to the ISSUE_TEMPLATE/ dir and adding required YAML frontmatter

• as originally reported in Errors duplicated in buildEnd hook #487 (comment)

Details

• move template and add required YAML frontmatter, per the issue template docs

  • had to figure out this syntax because it's not explicitly documented and the interactive chooser the docs say to use (e.g. https://github.com/agilgur5/rollup-plugin-typescript2/issues/templates/edit) didn't work either...
    • the template chooser doesn't work and throws an error in the console too...:

      Uncaught TypeError: Cannot read properties of null (reading 'content')
          at HTMLDivElement.capture (template-editor.ts:436:33)
      

    • eventually found a section in the issue forms docs that happens to show the syntax for issue template frontmatter
      • but no such example exists in the issue template docs..

• also add config.yml to disable blank issues

Verification

• tested against my own fork with a lot of (pretty frustrating) trial-and-error
  • (also had to temporarily enable issues and temporarily disable actions to not waste CI minutes testing this. not an ideal testing format, a branch preview would be very helpful...)

Historical Context

• the .github/issue_template.md single template was apparently silently removed by GitHub:
  • github/docs@21f56d5 has some docs removals
    • the GHE release note therein explicitly says it is no longer supported (but no announcement for GitHub.com?!?)
  • from our own issues, it appears to have been removed at some point between March 30th (#485) and May 3rd 2026 (#487)
    • it had been working at least since March 26th (#480)
      • (#485 was edited to use the template, so unsure if the prompt was seen initially or not)
  • it was reported to GitHub Docs on May 17th (.github/issue_template.md does not work anymore github/docs#44311) and removed from the docs on the 21st via github/docs@9e08905 / deprecate: .github/issue_template.md blank issues template github/docs#44312
    • that was apparently originally reported to Nix in NixOS/nixpkgs@556e57a / ISSUE_TEMPLATE: deprecate NixOS/nixpkgs#521074
    • Note that the word "deprecate" in these instances is incorrect -- it was entirely removed, with no deprecation nor deprecation warning

Misc Notes

• Note that issue forms are still in beta and still don't support custom markdown/HTML on output, so don't support the "spoiler" <details> tag we use to condense various sections
• GitHub has been breaking things left and right for many months now...