docs: add a pull request template

[Zaldaryon]

This repository has no .github/PULL_REQUEST_TEMPLATE.md. CONTRIBUTING.md's own guidance on the subject is one line: "include a summary of the changes made and why they are necessary." Every PR body against this repo has been reconstructed from the maintainer's own prose habits by reading past PRs, not prompted by anything the "Open a pull request" screen shows.

Stratum has a template. Its checklist is specific to Stratum's decompile-and-patch workflow (extract-patches.ps1, the // Stratum marker convention, no vanilla source committed) and none of it applies here, so this isn't a copy. Nimbus has no template file either, but its PRs share a real informal shape worth learning from: dense prose for the summary, and testing evidence given as actual numbers (test counts, coverage percentages, before-and-after numbers for a performance change) rather than a bare "tests pass."

What this template does:

• Summary and Testing as free text, matching how PRs against this repo already read, rather than boxing the explanation into checkboxes.
• Type as a quick classification (bug fix, feature, performance, refactor, tests only, docs), which Stratum's template has and this repo's history shows real use for (PR test(ipc): cover REMOVE_FILE_FROM_PATH #134 was tests-only, for one).
• Checklist using this repository's own five local gates instead of Stratum's: typecheck, lint:ci, format:check, test:coverage, build:unpack. These are the same five branch protection already requires on dev and main, so the checklist is a reminder to run them before pushing, not a new requirement.
• One line neither template has: a reminder that normal pull requests target dev, not main. That rule currently lives only in CONTRIBUTING.md's prose, nowhere a contributor filling out a PR would see it at the moment it matters.

One thing worth knowing before merging: GitHub reads pull request templates from the repository's default branch, which is main here, not dev. Landing this on dev (the normal target for every PR per CONTRIBUTING.md) means it will not show up on the "Open a pull request" screen until the next dev-to-main promotion. Flagging it rather than routing around the branch rule myself.

Type

• Docs or build

Checklist

• Targets dev, not main.
• No code changes, nothing to typecheck, lint, test, or build.

Testing

Not applicable, no code changed. Rendered the file locally to check the checkbox and heading markup displays as intended.

Related issues

None filed. Opened directly off a private-workspace observation while reviewing another PR's absence of guidance.

[Pixnop]

Approving. The template asks for exactly what this repo's review culture already demands, evidence over assertion, and the Testing section's 'not just tests pass' line plus the delete-this-line instruction keep it from fossilizing into checkbox theater. One optional refinement for a later pass: the Related issues line hardcodes Fixes, and this repo has twice needed Refs instead for PRs that deliberately address half an issue, so a one-line hint that Refs exists for partial work would save the next contributor the same lesson.