feat(agent-skills): install the wiki and consume vault skills

Source the wiki and consume skills from the skills flake, placing them
globally so they are active in every project. wiki reads the personal
Obsidian vault read-only, and consume mines a source into it, pairing
with the Obsidian vault this branch installs.

modules/agents/skills.nix

@@ -1,11 +1,20 @@
-{ config, inputs, ... }:
+{
+  config,
+  inputs,
+  pkgs,
+  ...
+}:
 # Global agent skills, placed under the skills directory so they are active in
 # every project.
 let
   user = config.user.name;
 
   # The skills installed globally, as derivations from the skills flake.
-  skills = [ ];
+  # wiki reads the personal Obsidian vault, and consume mines a source into it.
+  skills = with inputs.skills.packages.${pkgs.stdenv.hostPlatform.system}; [
+    wiki
+    consume
+  ];
 in
 {
   home-manager.sharedModules = [ inputs.skills.homeModules.default ];