test(tier2): add trivial smoke track for e2e test (force-added, fixture)

tests/artifacts/tier2_smoke_track/plan.md

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+# Implementation Plan: smoke track
+
+## Phase 1: Add the file
+
+- [ ] Task 1.1: Create `tests/artifacts/tier2_smoke_track/added.md` with content `smoke test ok\n`
+- [ ] Task 1.2: Commit with message `test(tier2): smoke e2e track`

tests/artifacts/tier2_smoke_track/spec.md

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+# Smoke Track: trivial doc-file addition
+
+## Overview
+
+A 1-task track that just adds a single doc file. Used by the smoke e2e
+test to verify the full Tier 2 pipeline (bootstrap + branch + commit).
+
+## Goals
+
+- Add `tests/artifacts/tier2_smoke_track/added.md` with one line of content
+- Commit the file on a feature branch
+- Verify the branch exists with 1 commit
+
+## Functional Requirements
+
+- FR1: create the file with content "smoke test ok\n"
+- FR2: commit with message "test(tier2): smoke e2e track"
+
+## Out of Scope
+
+- Anything else.