Add explicit PR template instructions in issue body and agent protocol

Address review feedback:
- Add '### PR template' section in generated issue body directing the
  agent to use ?template=coverage.md or copy template contents
- Update copilot-test-coverage.instructions.md PR requirements with
  explicit template usage instructions
- Validated script locally with mock data: below-threshold, above-
  threshold, and absolute-path normalization all pass correctly

Agent-Logs-Url: https://github.com/microsoft/vscode-cmake-tools/sessions/cb96c55e-0fc9-4e59-b0a8-a1fc704e2182

Co-authored-by: hanniavalera <90047725+hanniavalera@users.noreply.github.com>

Author: Copilot

.github/instructions/copilot-test-coverage.instructions.md

@@ -73,5 +73,5 @@ Do **not** open the PR unless every file listed in the issue has either:
 
 - Branch name: `coverage/<module-name>-tests`
 - Open as **ready for review** only after the self-audit checklist in the issue is fully checked
-- PR description must use `.github/PULL_REQUEST_TEMPLATE/coverage.md`
+- **PR description must use the coverage template**: copy the contents of `.github/PULL_REQUEST_TEMPLATE/coverage.md` into the PR body (or append `?template=coverage.md` to the PR creation URL). Fill in the coverage-delta table and check every self-audit box.
 - `CHANGELOG.md` must have one entry under `Improvements:`

.github/scripts/check-coverage-and-open-issue.mjs

@@ -150,6 +150,13 @@ New tests **must** go in \`test/unit-tests/backend/\` and run in plain Node.js (
 - Pure logic modules (\`expand.ts\`, \`shlex.ts\`, \`cache.ts\`, \`diagnostics/\`, \`preset.ts\`) are ideal targets.
 ${remainingNote}
 
+### PR template
+
+When opening the pull request, **you must use the coverage PR template**.
+Include \`?template=coverage.md\` in the PR creation URL, or copy the contents of
+\`.github/PULL_REQUEST_TEMPLATE/coverage.md\` into the PR description and fill in
+the coverage table and checklist.
+
 ### Constraints
 
 - Tests go in \`test/unit-tests/backend/\` — use Mocha \`suite\`/\`test\` with \`assert\`