chore: initial bootstrap — 5 reusable workflows + scaffolding

Public-readable Tier-1 exception (alongside sporel-meta) for the
practical reason that community pipelines need to call into these
workflows without per-repo deploy-token setup.

5 reusable workflows moved from sporel-meta/.gitea/workflows/ to here
(Plan-B.1: privacy-fix for sporel-meta which stays private with the
proprietary design docs).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/reusable-engine-launcher.yml

@@ -0,0 +1,59 @@
+# Reusable workflow: Engine + Launcher (Cat 1 per ADR-0025)
+# C-Build (Windows + Linux) → smoke tests → on-tag: release artefacts
+name: Engine + Launcher CI
+
+on:
+  workflow_call:
+    inputs:
+      build_type:
+        description: "CMake build type"
+        type: string
+        default: "Release"
+      smoke_test_script:
+        description: "Path to smoke-test script (relative to repo root); empty = skip"
+        type: string
+        default: "tests/smoke.sh"
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Configure CMake
+        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ inputs.build_type }}
+
+      - name: Build
+        run: cmake --build build --config ${{ inputs.build_type }} --parallel
+
+      - name: Smoke tests
+        if: hashFiles(inputs.smoke_test_script) != ''
+        shell: bash
+        run: |
+          chmod +x "${{ inputs.smoke_test_script }}" || true
+          "${{ inputs.smoke_test_script }}"
+
+      - name: Install (on tag)
+        if: startsWith(github.ref, 'refs/tags/')
+        run: cmake --install build --prefix=${{ github.workspace }}/install --config ${{ inputs.build_type }}
+
+      - name: Package release artefacts (on tag)
+        if: startsWith(github.ref, 'refs/tags/')
+        shell: bash
+        run: |
+          OS_TAG="${{ matrix.os }}"
+          OS_TAG="${OS_TAG//-latest/}"
+          ARTEFACT_NAME="${GITHUB_REPOSITORY##*/}-${GITHUB_REF_NAME}-${OS_TAG}.zip"
+          cd install && zip -r "../${ARTEFACT_NAME}" . && cd ..
+          echo "ARTEFACT_NAME=${ARTEFACT_NAME}" >> "$GITHUB_ENV"
+
+      - name: Upload to Gitea Release (on tag)
+        if: startsWith(github.ref, 'refs/tags/')
+        uses: akkuman/gitea-release-action@v1
+        with:
+          files: ${{ env.ARTEFACT_NAME }}