refactor: move docs transformOptions to clanLib to reduce rebuilds

- Add clanLib.docs.stripStorePathsFromDeclarations to deduplicate code
- Update all documentation generation to use the shared function
- This strips store paths from option declarations to prevent options.json
  from rebuilding when only store paths change but content remains the same
- Reduces unnecessary documentation rebuilds when making unrelated changes

lib/docs.nix

@@ -0,0 +1,21 @@
+{ lib, ... }:
+{
+  # Strip store paths from option declarations to make docs more stable
+  # This prevents documentation from rebuilding when store paths change
+  # but the actual content remains the same
+  stripStorePathsFromDeclarations = opt:
+    opt // {
+      declarations = map (decl:
+        if lib.isString decl && lib.hasPrefix "/nix/store/" decl then
+          let
+            parts = lib.splitString "/" decl;
+          in
+            if builtins.length parts > 4 then
+              "/" + lib.concatStringsSep "/" (lib.drop 4 parts)
+            else
+              decl
+        else
+          decl
+      ) opt.declarations;
+    };
+}