fix: remove broken eigent reference

The eigent package directory was deleted in 96f5d7f (which was titled
"chore: update n8n, openwork, vibetyper") but the callPackage reference
in pkgs/default.nix and the row in docs/packages/README.md were left
behind. As a result `nix build .#eigent` and `nix flake check` failed
with "undefined variable" errors when the eigent attribute was forced.

Drop both references so the package set evaluates cleanly.

docs/packages/README.md

@@ -15,7 +15,6 @@ These packages are built from source in `pkgs/<name>/`:
 | `sidecar` | Companion tool for CLI agents with diffs, file trees, and task management | Go | `pkgs/sidecar/` |
 | `td` | Minimalist CLI for tracking tasks across AI coding sessions | Go | `pkgs/td/` |
 | `code2prompt` | Convert code to prompts | Go | `pkgs/code2prompt/` |
-| `eigent` | Eigenvalue tool | Python | `pkgs/eigent/` |
 | `hyprpaper-random` | Random wallpaper setter for Hyprpaper | Shell | `pkgs/hyprpaper-random/` |
 | `kestractl` | CLI for Kestra workflow orchestration | Go | `pkgs/kestractl/` |
 | `launch-webapp` | Launch web applications | Shell | `pkgs/launch-webapp/` |