Add Copilot instructions for PR labeling

We have no `.github/copilot-instructions.md`, so agents opening PRs have no
guidance on labels. That matters because GitHub's auto-generated release notes
categorize merged PRs by their `Issue-*` label (see `.github/release.yml`):
`Issue-Enhancement` and `Issue-Bug` get their own sections, and everything
else falls through the `"*"` catch-all into "Other Changes 🙏". A PR with no
`Issue-*` label is silently miscategorized.

This adds a short "Pull Request Labels" policy: every PR needs at least one
`Area-*` label and exactly one `Issue-*` label, plus `OS-*` when relevant and
`Ignore` to exclude from the changelog. It references `.github/release.yml` as
the source of truth for the changelog mapping and tells readers to run
`gh label list` for the authoritative label set rather than hard-coding one
that will drift.

Drafted by Copilot (Claude Opus 4.8).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: andyleejordan

.github/copilot-instructions.md

@@ -0,0 +1,37 @@
+# Copilot Repository Instructions
+
+## Pull Request Labels
+
+Every pull request **must** be labeled before it is opened so it is triaged
+correctly and lands in the right changelog section.
+
+Each PR requires:
+
+- **At least one `Area-*` label** describing the part of the codebase it touches
+  (e.g. `Area-Debugging`, `Area-Language Server`, `Area-Workspaces`,
+  `Area-Documentation`). This is used for triage and filtering.
+- **Exactly one `Issue-*` label** describing the kind of change:
+  - `Issue-Bug` — a bug fix.
+  - `Issue-Enhancement` — a new feature or changed behavior.
+  - `Issue-Performance` — a performance improvement.
+
+The `Issue-*` label is not optional: GitHub's auto-generated release notes use it
+to pick the changelog category. See [`.github/release.yml`](./release.yml) for the
+authoritative mapping (`Issue-Enhancement` → "Enhancements & Features ✨",
+`Issue-Bug` → "Squashed Bugs 🐛"). Any PR **without** an `Issue-*` label falls
+through the `"*"` catch-all into "Other Changes 🙏" and is silently
+miscategorized, so always set one correctly.
+
+Additionally:
+
+- Add the relevant **`OS-*` label** (`OS-Windows`, `OS-macOS`, `OS-Linux`) when a
+  change is platform-specific.
+- Use the **`Ignore`** label only for changes that should be excluded from the
+  release notes entirely (e.g. pure CI, test, or docs chores the maintainers do
+  not want in the changelog). `.github/release.yml` excludes this label from the
+  changelog.
+
+The full, authoritative set of labels drifts over time — do not hard-code it
+here. List the current labels with `gh label list --repo PowerShell/PowerShellEditorServices`
+or the repo's [Labels page](https://github.com/PowerShell/PowerShellEditorServices/labels)
+and pick the closest matches.