Rewrite in Go: static binaries, zero runtime dependencies

Replace Node.js + Python codebase with three Go binaries:
- claude-statusline: CLI status bar for Claude Code
- claude-fetcher: standalone cron job for API usage
- claude-widget: system tray icon (fyne-io/systray + fogleman/gg)

All CGO-free for trivial cross-compilation. Add nfpm .deb packaging
with autostart and cron. CI pipeline produces Linux + Windows binaries,
.deb, .tar.gz, and .zip release assets.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packaging/nfpm.yaml

@@ -0,0 +1,43 @@
+name: claude-statusline
+arch: amd64
+platform: linux
+version: "${VERSION}"
+section: utils
+priority: optional
+maintainer: Axel Meyer <axel.meyer@durania.net>
+description: |
+  Claude API usage monitor — CLI statusline, cron fetcher, and desktop tray widget.
+  Shows 5-hour and 7-day token usage from claude.ai in your terminal or system tray.
+vendor: davoryn.de
+homepage: https://git.davoryn.de/calic/claude-statusline
+license: MIT
+
+contents:
+  - src: ./claude-statusline
+    dst: /usr/bin/claude-statusline
+    file_info:
+      mode: 0755
+
+  - src: ./claude-fetcher
+    dst: /usr/bin/claude-fetcher
+    file_info:
+      mode: 0755
+
+  - src: ./claude-widget
+    dst: /usr/bin/claude-widget
+    file_info:
+      mode: 0755
+
+  - src: ./packaging/linux/claude-widget.desktop
+    dst: /etc/xdg/autostart/claude-widget.desktop
+    file_info:
+      mode: 0644
+
+  - src: ./packaging/linux/claude-statusline-fetch
+    dst: /etc/cron.d/claude-statusline-fetch
+    file_info:
+      mode: 0644
+
+scripts:
+  postinstall: ./packaging/linux/postinstall.sh
+  preremove: ./packaging/linux/preremove.sh