refactor: group stow packages into common, mac and kde

Split the packages by platform so each app stays an opt-in Stow package
under common/, mac/ or kde/. KDE gets its own Fastfetch, Helium and
Spectacle packages, and darwin-breeze becomes kde/theme. The READMEs
document stowing a whole group as well as individual packages.

common/git/.config/git/config

@@ -0,0 +1,22 @@
+[init]
+	defaultBranch = main
+
+[user]
+	name = Tri Vo Khac
+	email = git@trivk.dev
+
+[core]
+	compression = 9
+	whitespace = error
+	preloadindex = true
+
+[advice]
+	addEmptyPathspec = false
+	pushNonFastForward = false
+	statusHints = false
+
+[push]
+	autoSetupRemote = true
+
+[url "git@github.com:"]
+	insteadOf = "gh:"

common/git/.config/git/ignore

@@ -0,0 +1 @@
+**/.claude/settings.local.json