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/linux/org.darksingularity.OrbitHub.metainfo.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<component type="desktop-application">
+  <id>org.darksingularity.OrbitHub</id>
+  <name>OrbitHub</name>
+  <summary>Unified remote session manager for SSH and RDP</summary>
+  <metadata_license>MIT</metadata_license>
+  <project_license>MIT</project_license>
+  <description>
+    <p>OrbitHub is a native desktop app for organizing connection profiles and launching SSH and RDP sessions in one tabbed interface.</p>
+  </description>
+  <launchable type="desktop-id">org.darksingularity.OrbitHub.desktop</launchable>
+  <url type="homepage">https://git.darksingularity.org/DarkSingularity/orbithub</url>
+  <provides>
+    <binary>orbithub</binary>
+  </provides>
+</component>