feat: add integration tests and GitHub Actions CI

Add integration test files for all providers (apt, dpkg, pacman, apk,
dnf, rpm, flatpak, snap, pkg, detect) behind the 'integration' build
tag. Tests exercise real package operations: update, search, info,
install, verify, list, remove, and capability interfaces.

Add GitHub Actions workflow running unit tests on ubuntu-latest and
integration tests on Debian, Ubuntu, Fedora, Alpine, Arch Linux, and
Ubuntu+Flatpak containers/runners.

.github/workflows/integration.yml

@@ -0,0 +1,118 @@
+name: Integration Tests
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  unit-tests:
+    name: Unit Tests
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - run: go build ./...
+      - run: go vet ./...
+      - run: go test -race ./...
+
+  debian:
+    name: Debian (apt)
+    runs-on: ubuntu-latest
+    container: debian:bookworm
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - name: Setup
+        run: |
+          apt-get update
+          apt-get install -y sudo tree curl
+      - name: Integration tests
+        run: go test -v -tags integration -count=1 ./apt/ ./dpkg/ ./detect/
+
+  ubuntu:
+    name: Ubuntu (apt + snap)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - name: Setup
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y tree
+          sudo snap install hello-world 2>/dev/null; sudo snap remove hello-world 2>/dev/null
+      - name: Integration tests (apt)
+        run: sudo -E go test -v -tags integration -count=1 ./apt/ ./dpkg/ ./detect/
+      - name: Integration tests (snap)
+        run: sudo -E go test -v -tags integration -count=1 ./snap/
+
+  fedora:
+    name: Fedora (dnf)
+    runs-on: ubuntu-latest
+    container: fedora:latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - name: Setup
+        run: |
+          dnf install -y tree sudo
+      - name: Integration tests
+        run: go test -v -tags integration -count=1 ./dnf/ ./rpm/ ./detect/
+
+  alpine:
+    name: Alpine (apk)
+    runs-on: ubuntu-latest
+    container: alpine:latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - name: Setup
+        run: |
+          apk add --no-cache sudo tree bash
+      - name: Integration tests
+        run: go test -v -tags integration -count=1 ./apk/ ./detect/
+
+  arch:
+    name: Arch Linux (pacman)
+    runs-on: ubuntu-latest
+    container: archlinux:latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - name: Setup
+        run: |
+          pacman -Syu --noconfirm
+          pacman -S --noconfirm sudo tree
+      - name: Integration tests
+        run: go test -v -tags integration -count=1 ./pacman/ ./detect/
+
+  flatpak:
+    name: Ubuntu + Flatpak
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+      - name: Verify flatpak not installed
+        run: |
+          if command -v flatpak &>/dev/null; then echo "already installed"; else echo "not installed — good"; fi
+      - name: Install flatpak
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y flatpak
+          sudo flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
+      - name: Integration tests
+        run: sudo -E go test -v -tags integration -count=1 ./flatpak/