flake.nix: add kanjivg as input, remove assets/kanjivg git submodule

.gitmodules

@@ -1,3 +0,0 @@
-[submodule "assets/kanjivg"]
-	path = assets/kanjivg
-	url = git@github.com:KanjiVG/kanjivg.git

flake.lock

@@ -1,5 +1,21 @@
 {
   "nodes": {
+    "kanjivg": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1754131552,
+        "narHash": "sha256-1h3nT1f1QqXme4rU3HMmEREn74sAASyZ8qzjZ0tPi4I=",
+        "owner": "KanjiVG",
+        "repo": "kanjivg",
+        "rev": "0d08020e69611552a0fbe13d49365d6196431b96",
+        "type": "github"
+      },
+      "original": {
+        "owner": "KanjiVG",
+        "repo": "kanjivg",
+        "type": "github"
+      }
+    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1754214453,
@@ -17,6 +33,7 @@
     },
     "root": {
       "inputs": {
+        "kanjivg": "kanjivg",
         "nixpkgs": "nixpkgs"
       }
     }

flake.nix

@@ -3,11 +3,17 @@
 
   inputs = {
     nixpkgs.url = "nixpkgs/nixos-unstable";
+
+    kanjivg = {
+      url = "github:KanjiVG/kanjivg";
+      flake = false;
+    };
   };
 
   outputs = {
     self,
     nixpkgs,
+    kanjivg
   }: let
     inherit (nixpkgs) lib;
     systems = [
@@ -25,6 +31,8 @@
           flutter
           dart
         ];
+
+        env.KANJIVG_PATH = "${kanjivg}/kanji";
       };
     });