packaging: rename app ID to org.darksingularity.OrbitHub

The reverse-DNS app ID should reflect a domain we actually control.
Renames the desktop file, AppStream metainfo, icon, Flatpak manifest,
and macOS bundle identifier from io.orbithub.OrbitHub to
org.darksingularity.OrbitHub. Also fixes a stale homepage URL in the
metainfo file pointing at an old git host.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packaging/flatpak/org.darksingularity.OrbitHub.yml

@@ -0,0 +1,21 @@
+app-id: org.darksingularity.OrbitHub
+runtime: org.kde.Platform
+runtime-version: "6.10"
+sdk: org.kde.Sdk
+command: orbithub
+finish-args:
+  - --share=network
+  - --share=ipc
+  - --socket=fallback-x11
+  - --socket=wayland
+  - --device=dri
+  - --filesystem=home
+modules:
+  - name: orbithub
+    buildsystem: cmake-ninja
+    builddir: true
+    config-opts:
+      - -DCMAKE_BUILD_TYPE=Release
+    sources:
+      - type: dir
+        path: ../..