Migrate Angular 2 to Angular 19 with standalone components

- Upgrade Angular, Firebase, and AngularFire to latest versions
- Replace NgModules with standalone components and bootstrapApplication
- Replace angular-cli.json with angular.json and ESLint
- Add Firebase App Check with reCAPTCHA v3 for abuse protection
- Move Firebase config out of version control (firebaseConfig.example.ts)
- Fix AngularFire injection context errors using runInInjectionContext
- Implement drag-and-drop reordering within and across columns
- Add inline editing for card title and description
- Add subtask deletion with confirmation modal
- Refresh UI with modern card-based look and feel

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

eslint.config.js

@@ -0,0 +1,44 @@
+// @ts-check
+const eslint = require("@eslint/js");
+const { defineConfig } = require("eslint/config");
+const tseslint = require("typescript-eslint");
+const angular = require("angular-eslint");
+
+module.exports = defineConfig([
+  {
+    files: ["**/*.ts"],
+    extends: [
+      eslint.configs.recommended,
+      tseslint.configs.recommended,
+      tseslint.configs.stylistic,
+      angular.configs.tsRecommended,
+    ],
+    processor: angular.processInlineTemplates,
+    rules: {
+      "@angular-eslint/directive-selector": [
+        "error",
+        {
+          type: "attribute",
+          prefix: "app",
+          style: "camelCase",
+        },
+      ],
+      "@angular-eslint/component-selector": [
+        "error",
+        {
+          type: "element",
+          prefix: "app",
+          style: "kebab-case",
+        },
+      ],
+    },
+  },
+  {
+    files: ["**/*.html"],
+    extends: [
+      angular.configs.templateRecommended,
+      angular.configs.templateAccessibility,
+    ],
+    rules: {},
+  }
+]);