chore(opencode): update to v1.1.51 and refactor build configuration

- Update opencode from v1.1.48 to v1.1.51
- Refactor build dependencies: remove fzf, add sysctl conditionally for Darwin
- Fix bun to use nixpkgs-unstable input instead of direct dependency
- Add platform-specific outputHash for Darwin and Linux
- Move wrapProgram from postFixup to installPhase
- Remove unnecessary build patch and postPatch/postBuild workarounds
- Fix config path to use absolute home directory
- Add git and home-manager to default shell inputs
- Minor README documentation reordering

shells/default/default.nix

@@ -19,8 +19,10 @@ pkgs.mkShell {
   name = "reichard-dev";
 
   buildInputs = with pkgs; [
-    rsync
     age
+    git
+    home-manager
+    rsync
     ssh-to-age
     sync-repo
   ];