feat: Add Renovate configuration for dependency tracking

renovate.json

@@ -0,0 +1,38 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "timezone": "America/Los_Angeles",
+  "nix": {
+    "enabled": true
+  },
+  "lockFileMaintenance": {
+    "enabled": true,
+    "schedule": ["before 5am on monday"]
+  },
+  "dependencyDashboard": true,
+  "dependencyDashboardTitle": "NixOS Configs Dependency Dashboard",
+  "packageRules": [
+    {
+      "description": "Group all GitHub Actions updates",
+      "matchManagers": ["github-actions"],
+      "groupName": "github-actions"
+    },
+    {
+      "description": "Group stable NixOS ecosystem inputs",
+      "matchManagers": ["nix"],
+      "matchPackagePatterns": ["^nixpkgs$", "^home-manager$", "^nix-darwin$"],
+      "groupName": "nix-stable-ecosystem"
+    },
+    {
+      "description": "Group unstable NixOS ecosystem inputs",
+      "matchManagers": ["nix"],
+      "matchPackagePatterns": ["nixpkgs-unstable", "home-manager-unstable"],
+      "groupName": "nix-unstable-ecosystem"
+    },
+    {
+      "description": "Ignore private Gitea inputs (handle separately)",
+      "matchManagers": ["nix"],
+      "matchPackagePatterns": ["google-cookie-retrieval"],
+      "enabled": false
+    }
+  ]
+}