feat: add hooks.biome.settings.flags for extra CLI flags

Mirrors the existing 'black' hook pattern so users can pass arbitrary
CLI flags such as --no-errors-on-unmatched (commonly needed when staged
files are all excluded by biome's own config, e.g. dep-only or generated-
file-only commits).

Unblocks workarounds that override hooks.biome.entry via lib.mkForce.

Author: lew

modules/hooks.nix

@@ -216,6 +216,13 @@ in
               # underlying biome binary (i.e biome.json if exists)
               default = "";
             };
+
+            flags = mkOption {
+              type = types.str;
+              description = "Additional flags passed to biome. See all available [here](https://biomejs.dev/reference/cli/).";
+              default = "";
+              example = "--no-errors-on-unmatched";
+            };
           };
         };
       };
@@ -2669,6 +2676,7 @@ in
                 mkCmdArgs [
                   [ (hooks.biome.settings.write) "--write" ]
                   [ (hooks.biome.settings.configPath != "") "--config-path ${hooks.biome.settings.configPath}" ]
+                  [ (hooks.biome.settings.flags != "") hooks.biome.settings.flags ]
                 ];
             in
             "${binPath} check ${cmdArgs}";