feat: initial implementation of WooList phpList Integration plugin v1.0.0

- phpList REST API wrapper with subscriber get-or-create + list assignment
- WooCommerce Settings tab (5 sections: connection, orders, signup, newsletter)
- Test Connection button via admin-post action
- Hooks for order completed/cancelled and user_register events
- [woolist_newsletter] shortcode with jQuery AJAX, fixed & auto-generated coupons
- Responsive front-end form styles and JS with loading/success/error states

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

woolist-phplist/assets/css/woolist-public.css

@@ -0,0 +1,88 @@
+/* ==========================================================================
+   WooList — Newsletter Form Styles
+   ========================================================================== */
+
+.woolist-newsletter-wrap {
+	max-width: 480px;
+	margin: 1.5em auto;
+	font-family: inherit;
+}
+
+/* Form row: input + button side by side */
+.woolist-form-row {
+	display: flex;
+	gap: 0.5em;
+	flex-wrap: wrap;
+}
+
+.woolist-email-input {
+	flex: 1 1 auto;
+	min-width: 0;
+	padding: 0.65em 0.9em;
+	font-size: 1em;
+	border: 1px solid #ccc;
+	border-radius: 4px;
+	outline: none;
+	transition: border-color 0.2s ease;
+	box-sizing: border-box;
+}
+
+.woolist-email-input:focus {
+	border-color: #0071a1;
+	box-shadow: 0 0 0 2px rgba(0, 113, 161, 0.15);
+}
+
+.woolist-submit-btn {
+	flex: 0 0 auto;
+	padding: 0.65em 1.4em;
+	font-size: 1em;
+	font-weight: 600;
+	color: #fff;
+	background-color: #0071a1;
+	border: none;
+	border-radius: 4px;
+	cursor: pointer;
+	transition: background-color 0.2s ease, opacity 0.2s ease;
+	white-space: nowrap;
+}
+
+.woolist-submit-btn:hover {
+	background-color: #005f8a;
+}
+
+.woolist-submit-btn:disabled {
+	opacity: 0.6;
+	cursor: not-allowed;
+}
+
+/* Response message area */
+.woolist-response {
+	margin-top: 0.85em;
+	padding: 0.75em 1em;
+	border-radius: 4px;
+	font-size: 0.95em;
+	line-height: 1.5;
+}
+
+.woolist-response.woolist-success {
+	background-color: #edfaf1;
+	border: 1px solid #52c41a;
+	color: #2d6a0f;
+}
+
+.woolist-response.woolist-error {
+	background-color: #fff1f0;
+	border: 1px solid #ff4d4f;
+	color: #a8071a;
+}
+
+/* Responsive: stack on very small screens */
+@media (max-width: 360px) {
+	.woolist-form-row {
+		flex-direction: column;
+	}
+
+	.woolist-submit-btn {
+		width: 100%;
+	}
+}