Implement XBPS proof of concept (issue #83)

Prove signed XBPS installation and immediate updates through Gitea.

Changes:
- Add scripts/xbps-publish.sh for automated XBPS publication
- Add Makefile targets: package-xbps, sign-xbps, xbps-publish
- Add docs/spec/xbps-proof-results.md with acceptance criteria results
- Add docs/adr/0008-native-void-support.md (architecture decision)
- Add docs/spec/native-void-support.md (feature specification)
- Add docs/spec/native-void-tickets.md (implementation tickets)

Proof results:
- Raw URL delivery verified (no LFS indirection)
- Signing key handling established (SSH RSA via xbps-rindex)
- Install and update flow demonstrated (v0.3.5 → v0.3.6)
- Cache behavior documented (6-hour max-age, -S flag for immediate discovery)
- Publication mechanism documented and automated
- Failure recovery demonstrated (git revert)

Repository: https://git.bongbetic.com/xavierk/Fenris-xbps

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>

Makefile

@@ -18,7 +18,7 @@ MANIFEST := $(DATA_DIR)/manifest.txt
 # Legacy history path (IN-4)
 LEGACY_HISTORY := ./data/history.jsonl
 
-.PHONY: help install upgrade uninstall purge update-deps test lint check-python check-smartctl import-legacy stage package-deb package-rpm package generate-test-key sign-rpm checksums clearsign release release-run release-dry-run clean
+.PHONY: help install upgrade uninstall purge update-deps test lint check-python check-smartctl import-legacy stage package-deb package-rpm package-xbps package generate-test-key sign-rpm sign-xbps checksums clearsign release release-run release-dry-run xbps-publish xbps-publish-dry-run clean
 
 help:
 	@echo "Fenris NVMe endurance monitor"
@@ -35,6 +35,8 @@ help:
 	@echo "  package      - Build deb + rpm packages"
 	@echo "  package-deb  - Build deb package only"
 	@echo "  package-rpm  - Build rpm package only"
+	@echo "  package-xbps - Build XBPS package only"
+	@echo "  sign-xbps    - Sign XBPS package with signing key"
 	@echo "  generate-test-key  - Create throwaway GPG key for CI/testing"
 	@echo "  sign-rpm     - Sign RPM payload with packaging key"
 	@echo "  checksums    - Generate SHA256SUMS manifest"
@@ -42,6 +44,8 @@ help:
 	@echo "  release      - Full release (build, sign, checksum, print upload steps)"
 	@echo "  release-run  - Execute the full release flow via scripts/release.sh"
 	@echo "  release-dry-run - Dry-run of the release flow (prints commands only)"
+	@echo "  xbps-publish - Publish XBPS package to distribution repository"
+	@echo "  xbps-publish-dry-run - Dry-run of XBPS publication (prints commands only)"
 	@echo "  clean        - Remove build artifacts"
 
 # ─── Pre-install gates ──────────────────────────────────────────────────────
@@ -257,6 +261,35 @@ package-rpm: stage
 package: package-deb package-rpm
 	@echo "=== Both packages built in dist/ ==="
 
+# ─── XBPS packaging (ADR 0008) ─────────────────────────────────────────────
+
+XBPS_SIGNING_KEY ?= $(HOME)/.ssh/id_rsa
+XBPS_SIGNED_BY ?= Fenris Packaging <packaging@bongbetic.com>
+
+package-xbps: stage
+	@echo "=== Building XBPS package ==="
+	xbps-create -A x86_64 \
+		-n fenris-$(FENRIS_VERSION)_1 \
+		-s "Fenris NVMe wear monitor" \
+		-S "NVMe wear monitor with persistent TUI" \
+		-m "Fenris Packaging <packaging@bongbetic.com>" \
+		-H "https://git.bongbetic.com/xavierk/Fenris" \
+		-l "MIT" \
+		build/stage
+	@echo "=== XBPS package built: fenris-$(FENRIS_VERSION)_1.x86_64.xbps ==="
+
+sign-xbps: package-xbps
+	@echo "=== Signing XBPS package ==="
+	xbps-rindex --sign-pkg --privkey $(XBPS_SIGNING_KEY) \
+		fenris-$(FENRIS_VERSION)_1.x86_64.xbps
+	@echo "=== XBPS package signed ==="
+
+xbps-publish:
+	bash scripts/xbps-publish.sh --publish
+
+xbps-publish-dry-run:
+	bash scripts/xbps-publish.sh --dry-run
+
 # ─── GPG key management ─────────────────────────────────────────────────────
 
 generate-test-key: