feat: config files, settings screen, hardware check

- Add config.py with multi-source config (YAML, .env, env vars)
- Add .env.example and config.yaml.example
- Add settings API endpoints (GET/POST /api/v1/settings)
- Add status endpoint (GET /api/v1/status) with hardware subsystem check
- Add settings screen to web client (protected by API token)
- Add localization strings for settings UI
- Add tests for config module and new endpoints
- Update README with config documentation

client/style.css

@@ -342,6 +342,107 @@ body {
 	overflow-x: hidden;
 }
 
+/* Settings button */
+.settings-btn {
+	position: absolute;
+	top: 10px;
+	right: 10px;
+	background: var(--bg);
+	color: var(--fg);
+	border: 2px solid var(--border);
+	width: 40px;
+	height: 40px;
+	font-size: 1.2em;
+	cursor: pointer;
+	z-index: 100;
+	font-family: inherit;
+}
+
+/* Settings screen */
+#settings-screen {
+	justify-content: flex-start;
+	padding-top: 40px;
+}
+
+#settings-screen h1 {
+	font-size: 1.5em;
+	border-bottom: 2px solid var(--border);
+	padding-bottom: 8px;
+	margin-bottom: 12px;
+}
+
+#settings-screen p {
+	margin-bottom: 12px;
+	color: var(--dim);
+}
+
+#settings-token-input {
+	background: var(--bg);
+	color: var(--fg);
+	border: 2px solid var(--border);
+	padding: 10px;
+	width: 100%;
+	margin-bottom: 10px;
+	font-family: inherit;
+	font-size: 1em;
+}
+
+#settings-access-btn,
+#settings-save-btn,
+#settings-back-btn {
+	background: var(--bg);
+	color: var(--fg);
+	border: 2px solid var(--border);
+	padding: 10px 20px;
+	font-size: 1em;
+	cursor: pointer;
+	margin-right: 10px;
+	margin-bottom: 10px;
+	font-family: inherit;
+}
+
+#settings-content {
+	margin-top: 20px;
+}
+
+#settings-content .panel {
+	margin-bottom: 15px;
+}
+
+#settings-content h2 {
+	font-size: 0.9em;
+	margin-bottom: 8px;
+	color: var(--dim);
+}
+
+#settings-pin,
+#settings-token {
+	background: var(--bg);
+	color: var(--fg);
+	border: 2px solid var(--border);
+	padding: 10px;
+	width: 100%;
+	font-family: inherit;
+	font-size: 1em;
+}
+
+#settings-status {
+	margin-top: 15px;
+	padding: 10px;
+	border: 2px solid var(--border);
+	background: var(--panel-bg);
+}
+
+.status {
+	color: var(--fg);
+}
+
+.error {
+	color: var(--dim);
+	font-size: 0.9em;
+	margin-top: 10px;
+}
+
 /* E-Ink specific: no transitions, sharp edges */
 * {
 	transition: none !important;