feat(\db-tool\): introduce unified db-tool package with postgres harness and tests (T0-T8)

package/db-tool/default.nix

@@ -0,0 +1,62 @@
+{ dash, hectic, postgresql_17, neovim, openssh, coreutils, gawk, lib }:
+let
+  shell = "${dash}/bin/dash";
+
+  database = hectic.writeShellApplication {
+    inherit shell;
+    bashOptions = [
+      "errexit"
+      "nounset"
+    ];
+    # SC2209: false positive — PAGER_OR_CAT=cat stores the string "cat" intentionally
+    excludeShellChecks = [ "SC2209" ];
+    name = "database";
+    runtimeInputs = [ hectic.migrator hectic.parse-uri postgresql_17 neovim openssh coreutils gawk ];
+
+    text = ''
+      ${builtins.readFile hectic.helpers.posix-shell.log}
+      ${builtins.readFile hectic.helpers.posix-shell.change_namespace}
+      ${builtins.readFile hectic.helpers.posix-shell.quote}
+      ${builtins.readFile hectic.helpers.posix-shell.pager_or_cat}
+      ${builtins.readFile ./database.sh}
+    '';
+
+    meta = {
+      description = "PostgreSQL development database management";
+      mainProgram = "database";
+    };
+  };
+
+  postgresInit = hectic.writeShellApplication {
+    inherit shell;
+    bashOptions = [ ];
+    name = "postgres-init";
+    runtimeInputs = [ postgresql_17 coreutils ];
+
+    text = builtins.readFile ./postgres-init.sh;
+
+    meta = {
+      description = "Initialize local PostgreSQL instance";
+      mainProgram = "postgres-init";
+    };
+  };
+
+  postgresCleanup = hectic.writeShellApplication {
+    inherit shell;
+    bashOptions = [ ];
+    name = "postgres-cleanup";
+    runtimeInputs = [ postgresql_17 coreutils ];
+
+    text = builtins.readFile ./postgres-cleanup.sh;
+
+    meta = {
+      description = "Clean up local PostgreSQL instance";
+      mainProgram = "postgres-cleanup";
+    };
+  };
+in
+{
+  "db-tool"          = database;
+  "postgres-init"    = postgresInit;
+  "postgres-cleanup" = postgresCleanup;
+}