chore(devshell): add test shell without static glibc

The default shell links cgo statically against glibc.static for the
production gitea binary. Test binaries built in that shell segfault
inside cgo NSS calls (getaddrinfo/getpwuid_r) because the static glibc
NSS modules need matching dynamic libs at runtime.

Split the shell:
- `nix develop`           -> production build shell (static, unchanged)
- `nix develop .#test`    -> test/dev shell, no static glibc

Verified: TestAPIProjects passes in the `test` shell.

flake.nix

@@ -27,8 +27,6 @@
     {
       devShells = forEachSupportedSystem (
         { pkgs, ... }:
-        {
-          default =
         let
           inherit (pkgs) lib;
 
@@ -38,20 +36,7 @@
           python3 = pkgs.python314;
           pnpm = pkgs.pnpm_10;
 
-              # Platform-specific dependencies
-              linuxOnlyInputs = lib.optionals pkgs.stdenv.isLinux [
-                pkgs.glibc.static
-              ];
-
-              linuxOnlyEnv = lib.optionalAttrs pkgs.stdenv.isLinux {
-                CFLAGS = "-I${pkgs.glibc.static.dev}/include";
-                LDFLAGS = "-L ${pkgs.glibc.static}/lib";
-              };
-            in
-            pkgs.mkShell {
-              packages =
-                with pkgs;
-                [
+          commonPackages = with pkgs; [
             # generic
             git
             git-lfs
@@ -79,17 +64,36 @@
             golangci-lint
             govulncheck
             tea
-                ]
-                ++ linuxOnlyInputs;
+          ];
 
-              env = {
+          commonEnv = {
             GO = "${go}/bin/go";
             GOROOT = "${go}/share/go";
-
             TAGS = "";
+          };
+        in
+        {
+          # production build shell: cgo links statically against glibc.static
+          default = pkgs.mkShell {
+            packages =
+              commonPackages
+              ++ lib.optionals pkgs.stdenv.isLinux [ pkgs.glibc.static ];
+
+            env =
+              commonEnv
+              // {
                 STATIC = "true";
               }
-              // linuxOnlyEnv;
+              // lib.optionalAttrs pkgs.stdenv.isLinux {
+                CFLAGS = "-I${pkgs.glibc.static.dev}/include";
+                LDFLAGS = "-L ${pkgs.glibc.static}/lib";
+              };
+          };
+
+          # test/dev shell: no static glibc — avoids cgo NSS segfaults in `go test`
+          test = pkgs.mkShell {
+            packages = commonPackages;
+            env = commonEnv;
           };
         }
       );