refactor(llm-agents): replace flattening overlay with upstream shared-nixpkgs

Drop the custom mkLlmAgentsOverlay factory (172 top-level attrs +
17-entry blocklist guarding against nixpkgs clobbering — the source of
the webcord buildNpmPackage and fetchPnpmDeps stack overflows).

Apply inputs.llm-agents.overlays.shared-nixpkgs directly instead. It
exposes everything under the pkgs.llm-agents.* namespace and clobbers
nothing, so the blocklist becomes unnecessary. Packages stay built
against this system's nixpkgs (allowUnfree), which qmd.override
cudaSupport in the m3-ares NVIDIA specialisation requires.

Consumers switched to namespaced refs:
- hosts/m3-hermes/services/hermes-agent.nix: herdr, opencode, qmd
- m3ta-home agents.nix (input bumped): agent-browser, beads, herdr,
  qmd, openspec — unqualified refs would now silently resolve to
  outdated nixpkgs attrs (opencode 0.3.x) or vanish.

openspec pass-through dropped from m3ta-nixpkgs (input bumped):
llm-agents is the single source of truth now.

Note: flake.nix/lock carry the pre-existing local path inputs for
m3ta-home and m3ta-nixpkgs (dev state, gitea URLs kept as comments).

Verified: drvPath evals for m3-hermes, m3-atlas, and the m3-ares
NVIDIA specialisation (qmd + CUDA EULA) all pass; statix/deadnix clean.

overlays/default.nix

@@ -48,56 +48,10 @@
     };
   };
 
-  # Factory: not a proper overlay itself — takes system to avoid the infinite
-  # recursion that occurs when accessing final/prev.system while the fixed-point
-  # is still being computed.  Exposed via outputs.lib, not outputs.overlays.
-  #
-  # Use llm-agents' shared-nixpkgs overlay so packages with optional GPU support
-  # (notably qmd) are built against this system's pkgs/config. Using the flake's
-  # pre-built `packages.${system}` set pins them to llm-agents' own nixpkgs,
-  # where allowUnfree is false; qmd.override { cudaSupport = true; } then fails
-  # on CUDA EULA packages during the m3-ares NVIDIA specialisation build.
-  #
-  # Keep the exposed top-level package names aligned with llm-agents' filtered
-  # flake packages, but take the package values from the shared package set.
-  # Filters out internal helpers (marked `passthru.hideFromDocs = true`
-  # upstream) that would otherwise clobber nixpkgs attributes. Most critically
-  # this excludes `buildNpmPackage` — llm-agents' buildNpmPackage is a guarded
-  # re-export whose `__functor`/`override` interaction with makeOverridable
-  # breaks any package (e.g. nixpkgs' webcord) that calls
-  # `buildNpmPackage.override { nodejs = ...; }`. See numtide/llm-agents.nix
-  # commit 40490259 and the wrapper at packages/buildNpmPackage/package.nix.
-  mkLlmAgentsOverlay = system: final: prev: let
-    sharedPackages = (inputs.llm-agents.overlays.shared-nixpkgs final prev).llm-agents or {};
-    exposedPackageNames =
-      builtins.filter
-      (name: inputs.nixpkgs.lib.hasAttrByPath [name] sharedPackages)
-      (builtins.attrNames (inputs.llm-agents.packages.${system} or {}));
-    exposedPackages =
-      builtins.listToAttrs
-      (map (name: {
-          inherit name;
-          value = sharedPackages.${name};
-        })
-        exposedPackageNames);
-  in
-    builtins.removeAttrs exposedPackages [
-      # Internal helpers from packages/* marked hideFromDocs upstream:
-      "antigravity"
-      "auto-claude"
-      "buildNpmPackage" # ← the culprit; breaks webcord's `buildNpmPackage.override { nodejs = ...; }`
-      "bun2nix"
-      "darwinOpenptyHook"
-      "default" # fzf launcher; collides with nothing in nixpkgs but kept out for hygiene
-      "dolt" # collides with nixpkgs.dolt (Dolt database); not used in this config
-      "flake-inputs"
-      "forge"
-      "formatelf"
-      "formatter" # collides conceptually with pkgs.formatter; not used here
-      "go-bin"
-      "unpinCargoMsrvHook"
-      "unpinGoModVersionHook"
-      "versionCheckHomeHook"
-      "wrapBuddy"
-    ];
+  # llm-agent packages (qmd, herdr, beads, …) come from
+  # inputs.llm-agents.overlays.shared-nixpkgs, applied directly in
+  # hosts/common/default.nix. They are consumed via the `pkgs.llm-agents.*`
+  # namespace — no flattening to top-level attributes (that clobbered
+  # nixpkgs attrs like buildNpmPackage/fetchPnpmDeps and needed a
+  # hard-to-maintain blocklist).
 }