CI: Add eslint and fix a few things

.eslintignore

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+src/pages/settings.svelte

.eslintrc.cjs

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+module.exports = {
+	env: {
+		browser: true,
+		es2021: true,
+	},
+	extends: ["eslint:recommended", "plugin:svelte/recommended"],
+	overrides: [
+		{
+			env: {
+				node: true,
+			},
+			files: [".eslintrc.{js,cjs}"],
+			parserOptions: {
+				sourceType: "script",
+			},
+		},
+		{
+			files: ["*.svelte"],
+			parser: "svelte-eslint-parser",
+		},
+	],
+	parserOptions: {
+		ecmaVersion: "latest",
+		sourceType: "module",
+	},
+	rules: {
+		"svelte/no-at-html-tags": "off",
+		// blocks while (true) { ... } loops
+		"no-constant-condition": "off",
+		// regex stuff i dont understand, and catches <a />
+		"no-useless-escape": "off",
+		"no-unused-vars": [
+			"error",
+			{
+				argsIgnorePattern: "^_",
+				varsIgnorePattern: "^_",
+				caughtErrorsIgnorePattern: "^_",
+			},
+		],
+		// empty catch blocks are fine
+		"no-empty": "off",
+		// spaces for minor indentation, tabs for major indentation
+		"no-mixed-spaces-and-tabs": "off",
+	},
+};

.github/workflows/eslint.yaml

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+# This workflow uses actions that are not certified by GitHub.
+# They are provided by a third-party and are governed by
+# separate terms of service, privacy policy, and support
+# documentation.
+# ESLint is a tool for identifying and reporting on patterns
+# found in ECMAScript/JavaScript code.
+# More details at https://github.com/eslint/eslint
+# and https://eslint.org
+
+name: ESLint
+
+on:
+  push:
+    branches: [ "develop", "main" ]
+  pull_request:
+    # The branches below must be a subset of the branches above
+    branches: [ "develop" ]
+  schedule:
+    - cron: '43 10 * * 2'
+
+jobs:
+  eslint:
+    name: Run eslint scanning
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      security-events: write
+      actions: read # only required for a private repository by github/codeql-action/upload-sarif to get the Action run status
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Install ESLint
+        run: |
+          npm install --group=dev
+          npm install eslint@8.10.0
+
+      - name: Run ESLint
+        run: npx eslint .
+          --config .eslintrc.cjs
+        continue-on-error: false