feat(hermes-agent): add mkOpencodeSkills integration for skills provisioning

- Add inputs parameter to module signature for flake input access
- Define hermesSkills via inputs.agents.lib.mkOpencodeSkills
- Includes customSkills from agents flake and external skills:
  - skills-basecamp (basecamp/basecamp-cli)
  - skills-anthropic (anthropics/skills)
  - skills-kestra (kestra-io/agent-skills)
- Verified with nixos-rebuild dry-run --flake .#m3-hermes (no errors)

hosts/m3-hermes/services/hermes-agent.nix

@@ -1,6 +1,7 @@
 {
   config,
   pkgs,
+  inputs,
   ...
 }: let
   # Default ElevenLabs voice: Bella (German-capable female)
@@ -12,6 +13,26 @@
   # site-packages via PYTHONPATH and provide libstdc++ for libolm (e2e).
   venvSitePackages = "/home/hermes/.venv/lib/python3.11/site-packages";
   gccLibPath = "${pkgs.stdenv.cc.cc.lib}/lib";
+
+  # Build skills using agents flake lib for hermes user
+  hermesSkills = inputs.agents.lib.mkOpencodeSkills {
+    inherit pkgs;
+    customSkills = "${inputs.agents}/skills";
+    externalSkills = [
+      {
+        src = inputs.skills-basecamp;
+        skillsDir = "skills";
+      }
+      {
+        src = inputs.skills-anthropic;
+        skillsDir = "skills";
+      }
+      {
+        src = inputs.skills-kestra;
+        skillsDir = "skills";
+      }
+    ];
+  };
 in {
   virtualisation.docker.enable = true;