fix(bootstrap): safe uninstall, add license, CI, and docs

- Fix uninstall to only remove own files (farmer/sprout can coexist)
- Add systemctl daemon-reload after removing unit files
- Suppress userdel error if user doesn't exist
- Add 0BSD LICENSE (matches gogrlx/grlx)
- Add GitHub Actions CI workflow (shellcheck)
- Expand README: non-interactive install, uninstall docs, arch list, badges

.github/workflows/ci.yml

@@ -0,0 +1,17 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  shellcheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install shellcheck
+        run: sudo apt-get install -y shellcheck
+      - name: Lint latest scripts
+        run: shellcheck latest/farmer latest/sprout