opencode: migrate programs.opencode.{settings => tui}.theme (#2268)

Migrate the deprecated programs.opencode.settings.theme declaration to
programs.opencode.tui.theme, following upstream commit [1] ("opencode:
add programs.opencode.tui option")

[1]: 1089b2caba

Closes: https://github.com/nix-community/stylix/issues/2264
Link: https://github.com/nix-community/stylix/pull/2268

Reviewed-by: Mirza Arnaut <mirza.arnaut45@gmail.com>
Reviewed-by: NAHO <90870942+trueNAHO@users.noreply.github.com>

flake/dev/flake.lock

@@ -118,11 +118,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1775223910,
-        "narHash": "sha256-QRdehpSKTttlZe0oY2n5OCfZeCMrHkKNlWF1LJzO9tY=",
+        "lastModified": 1775781825,
+        "narHash": "sha256-L5yKTpR+alrZU2XYYvIxCeCP4LBHU5jhwSj7H1VAavg=",
         "owner": "nix-community",
         "repo": "home-manager",
-        "rev": "f68887a4c11e662b0eb0323d34b3fb9506226719",
+        "rev": "e35c39fca04fee829cecdf839a50eb9b54d8a701",
         "type": "github"
       },
       "original": {

modules/opencode/hm.nix

@@ -8,7 +8,7 @@ mkTarget {
           theme = "stylix";
         in
         {
-          settings = { inherit theme; };
+          tui = { inherit theme; };
           themes.${theme} = {
             theme = {
               accent = {