refactor(wisdom): rename wisdomSimpleSlice to wisdomSlice

Rename the helper function `wisdomSimpleSlice` to `wisdomSlice` across
the codebase and update documentation to reflect the new naming
convention. This change simplifies the API for creating trivial
single-package slices.

modules/wisdom/editors/kate.nix

@@ -1,5 +1,5 @@
 { self, ... }: {
-  flake.homeManagerModules.wisdomEditorsKate = self.lib.wisdomSimpleSlice {
+  flake.homeManagerModules.wisdomEditorsKate = self.lib.wisdomSlice {
     path = "editors.kate";
     default = false;
     description = "Kate.";

modules/wisdom/editors/obsidian.nix

@@ -1,5 +1,5 @@
 { self, ... }: {
-  flake.homeManagerModules.wisdomEditorsObsidian = self.lib.wisdomSimpleSlice {
+  flake.homeManagerModules.wisdomEditorsObsidian = self.lib.wisdomSlice {
     path = "editors.obsidian";
     default = true;
     description = "Obsidian (unfree); skipped if unavailable here.";