Add machines.keys config and reorganize key structure

- Add config.machines.keys for machine-specific keys (private keys live on that machine)
- Move desktop SSH key to machines.keys.desktop.ssh
- Fix extractName to preserve "yubikey" (only strip .key/.pub extensions)
- Rename key files for clarity (android -> graphone, primary -> yubikey)
- Add age yubikey key for encrypted backups
- Add README files to document key purposes
- Update all machine configs to import system config

src/user/config/keys/default.nix

@@ -1,13 +1,17 @@
+{ lib }:
+
 with builtins;
 let
-  extractName = string:
+  extractName = filename:
     let
-      metadata = [
-        "pub" "public" "priv" "private"
-        "key" "file" "." "_" "-" "pk"
-      ];
-    in
-      replaceStrings metadata (builtins.map (_: "") metadata) string;
+      # Remove .key extension
+      noKey = lib.removeSuffix ".key" filename;
+      # Remove .pub/.priv/.public/.private markers
+      noMarkers = replaceStrings
+        [ ".pub" ".priv" ".public" ".private" ]
+        [ "" "" "" "" ]
+        noKey;
+    in noMarkers;
 
   constructKeys = dir: (
     listToAttrs (
@@ -17,7 +21,10 @@ let
           map (file: {
             name = extractName file;
             value = readFile "${dir}/${subdir}/${file}";
-          }) (filter (node: (readDir "${dir}/${subdir}").${node} == "regular") (attrNames (readDir "${dir}/${subdir}")))
+          }) (filter (file:
+            (readDir "${dir}/${subdir}").${file} == "regular" &&
+            lib.hasSuffix ".key" file
+          ) (attrNames (readDir "${dir}/${subdir}")))
         );
       }) (filter (node: (readDir dir).${node} == "directory") (attrNames (readDir dir)))
     )