fix(#2716): route non-user-facing conventional types to an Internal bucket, omit from release notes (#2838)

* test(#2716): failing-first regression for non-user-facing types → Internal bucket

* fix(#2716): route non-user-facing conventional types to an Internal bucket, omit from release notes

* fix(#2716): update SAMPLE_BODY/Discord/property tests for Internal bucket; fix stale CONTRIBUTING sentence (review)

* test(#2716): relax Discord Enhancement assertion (enhance: prefix not stripped by cleanBullet)

* docs(changeset): #2716 non-user-facing types omitted from release notes

* docs(changeset): backfill #2716 PR number to 2838

CONTRIBUTING.md

@@ -217,7 +217,7 @@ then run `scripts/release-notes/format-github-release-notes.cjs --apply` to
 rewrite the body into the project's curated format: an **Install** block,
 followed by **What's Changed** grouped into **Feature** / **Enhancement** /
 **Fix** sections (classified by each PR's conventional-commit title prefix —
-`feat` → Feature, `fix` → Fix, everything else → Enhancement), then
+`feat` → Feature, `fix` → Fix, non-user-facing types `test`/`chore`/`ci`/`docs`/`refactor`/`perf`/`revert` → omitted from the user-facing notes, everything else → Enhancement), then
 **New Contributors** and the **Full Changelog** link.
 
 To re-format an existing release by hand (e.g. backfilling an older release):
@@ -910,7 +910,7 @@ Defensive normalization at trust boundaries must validate both the value's type
 
 - **CommonJS** (`.cjs`) — the project uses `require()`, not ESM `import`
 - **No external dependencies in core** — `gsd-tools.cjs` and all lib files use only Node.js built-ins
-- **Conventional commits** — `feat:`, `fix:`, `docs:`, `refactor:`, `test:`, `ci:`. The full grammar is `<type>(<scope>): <subject>` (enforced by `hooks/gsd-validate-commit.sh`; subject ≤72 chars, lowercase, imperative mood, no trailing period). When the work resolves a tracked issue, put the issue number in the scope: `fix(#1520): randomize mktemp temp paths on BSD/macOS`. The same convention applies to PR titles — release notes are grouped by the title's type prefix (`feat` → Feature, `fix` → Fix, everything else → Enhancement).
+- **Conventional commits** — `feat:`, `fix:`, `docs:`, `refactor:`, `test:`, `ci:`. The full grammar is `<type>(<scope>): <subject>` (enforced by `hooks/gsd-validate-commit.sh`; subject ≤72 chars, lowercase, imperative mood, no trailing period). When the work resolves a tracked issue, put the issue number in the scope: `fix(#1520): randomize mktemp temp paths on BSD/macOS`. The same convention applies to PR titles — release notes are grouped by the title's type prefix (`feat` → Feature, `fix` → Fix, non-user-facing types omitted, everything else → Enhancement).
 
 ## File Structure