refactor(agents): consume llm-agents packages via pkgs.llm-agents namespace

numtide/llm-agents.nix's shared-nixpkgs overlay exposes everything under
pkgs.llm-agents.* — no flattening to top-level attrs anymore. Namespaced
refs fail loudly when the overlay is missing instead of silently falling
back to outdated nixpkgs attributes (opencode 0.3.x) or disappearing.

Requires the consumer's nixos-config to apply
inputs.llm-agents.overlays.shared-nixpkgs (see nixos-config
hosts/common/default.nix).

profiles/sets/coding/agents/agents.nix

@@ -61,23 +61,28 @@
     };
   };
 
+  # NOTE: llm-agent packages are consumed via the `llm-agents` namespace
+  # (pkgs.llm-agents.*), provided by numtide/llm-agents.nix's
+  # `overlays.shared-nixpkgs`. The consumer's nixos-config MUST apply that
+  # overlay — namespaced refs fail loudly if it is missing, instead of
+  # silently falling back to (outdated) nixpkgs attributes.
   home.packages = with pkgs; [
     agenix-cli
-    agent-browser
+    llm-agents.agent-browser
     m3taHomeInputs.agent-lib.packages.${pkgs.stdenv.hostPlatform.system}.agent-lib-cli
-    beads
+    llm-agents.beads
     buzz
     crunch
     docker-sbx
-    herdr
+    llm-agents.herdr
     pi-coding-agent
-    (qmd.override {
+    (llm-agents.qmd.override {
       vulkanSupport = videoDrivers == ["amdgpu"];
       cudaSupport = videoDrivers == ["nvidia"];
     })
     opencode-desktop
     openshell
-    openspec
+    llm-agents.openspec
     openwork
     talk
   ];