feat: scaffold Go project with flake.nix and directory structure

- Initialize go.mod with gitea.leeworks.dev/0xwheatyz/gitea-mobile
- Create directory structure: cmd/server/, internal/{config,gitea,handlers,middleware,templates}/, static/
- Add minimal HTTP server with /health and / endpoints
- Add flake.nix with Go toolchain, gopls, and air for live reload

Closes leeworks-agents/gitea-mobile#1

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

flake.nix

@@ -0,0 +1,31 @@
+{
+  description = "Gitea Mobile — mobile-first PWA for Gitea";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          buildInputs = with pkgs; [
+            go
+            gopls
+            gotools
+            go-tools
+            air
+          ];
+
+          shellHook = ''
+            echo "Gitea Mobile dev shell"
+            echo "  go $(go version | cut -d' ' -f3)"
+            echo "  air available for live reload: air"
+          '';
+        };
+      });
+}