chore(flake): add nix-index-database input

Prebuilt nix-index database (follows nixpkgs) so command-not-found works
immediately without a manual `nix-index` run. Consumed in shell.nix.
Lock change is purely additive; existing pins are unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

flake.lock

@@ -150,6 +150,26 @@
         "type": "github"
       }
     },
+    "nix-index-database": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1780816331,
+        "narHash": "sha256-0BYqs8yKWkOz2Q7+SP18N5E5gmDKSo6LSxIVIa0wWes=",
+        "owner": "nix-community",
+        "repo": "nix-index-database",
+        "rev": "1a2ea89c917781e88508d9fd2b507f2d2a0e173c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "nix-index-database",
+        "type": "github"
+      }
+    },
     "nixos-apple-silicon": {
       "inputs": {
         "flake-compat": "flake-compat",
@@ -231,6 +251,7 @@
         "home-manager": "home-manager",
         "nix-darwin": "nix-darwin",
         "nix-homebrew": "nix-homebrew",
+        "nix-index-database": "nix-index-database",
         "nixos-apple-silicon": "nixos-apple-silicon",
         "nixos-wsl": "nixos-wsl",
         "nixpkgs": "nixpkgs",

flake.nix

@@ -28,6 +28,12 @@
       url = "gitlab:rycee/nur-expressions?dir=pkgs/firefox-addons";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    # Prebuilt nix-index database so "command not found -> which package
+    # provides it" works immediately (no manual `nix-index` run). See shell.nix.
+    nix-index-database = {
+      url = "github:nix-community/nix-index-database";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
   outputs =