Add a PR template with a required "How to verify" section #359

The repo has no .github/PULL_REQUEST_TEMPLATE.md. CONTRIBUTING asks a PR for only "a brief description," while asking bug reports for "steps to reproduce" and "expected vs. actual behavior" — so a bug report is held to a higher reproducibility bar than the fix for it.

Proposal: add a PR template whose centerpiece is a required How to verify section — a reviewer-runnable before/after, and for behavior a unit test can't capture (wire output, a deployed channel, a REST path) the exact steps and observed result — plus a short checklist mirroring CONTRIBUTING and the contributor guardrails. Green CI tells a reviewer the build compiled; it doesn't tell them the fix works.

Raised by @pacmano1 during review of #343 (the mechanic who replaces the battery but never starts the car). Filing it as a tracked issue — and because the template itself will require one.