docs: add Pushover and improve push notification documentation (#27)

- Add Pushover to supported services list in UI
- Add Gotify to supported services list
- Add URL placeholder with examples (ntfy, pushover)
- Add link to shoutrrr.dev for all available services
- Change input type from 'url' to 'text' (shoutrrr URLs aren't HTTP URLs)
- Add comprehensive Push Notifications section to README
- Include URL examples for ntfy, Pushover, Gotify, Discord, Telegram

Closes feature request for Pushover support.

frontend/src/App.tsx

@@ -2243,12 +2243,12 @@ function AppContent() {
 														<span className="field-label">{t('settings.push.url')}</span>
 														<div className="input-with-tooltip">
 															<input
-																type="url"
+																type="text"
 																value={settings.shoutrrrUrl}
 																onChange={(e) => setSettings({ ...settings, shoutrrrUrl: e.target.value })}
-																placeholder="https://ntfy.sh/your-topic"
+																placeholder={t('settings.push.urlPlaceholder')}
 															/>
-															<span className="info-tooltip" data-tooltip={t('settings.push.supports')}>ⓘ</span>
+															<span className="info-tooltip" data-tooltip={`${t('settings.push.supports')}\n\n${t('settings.push.docsLink')}`}>ⓘ</span>
 														</div>
 													</label>
 												</div>

frontend/src/i18n/de.json

@@ -173,7 +173,9 @@
     },
     "push": {
       "url": "URL",
-      "supports": "Unterstützt ntfy, Discord, Telegram, Slack"
+      "urlPlaceholder": "ntfy://topic oder pushover://:token@userkey/",
+      "supports": "Unterstützt ntfy, Pushover, Gotify, Discord, Telegram, Slack & mehr",
+      "docsLink": "Siehe shoutrrr.dev für alle Services"
     },
     "schedule": {
       "title": "Erinnerungsplan",

frontend/src/i18n/en.json

@@ -175,7 +175,9 @@
     },
     "push": {
       "url": "URL",
-      "supports": "Supports ntfy, Discord, Telegram, Slack"
+      "urlPlaceholder": "ntfy://topic or pushover://:token@userkey/",
+      "supports": "Supports ntfy, Pushover, Gotify, Discord, Telegram, Slack & more",
+      "docsLink": "See shoutrrr.dev for all services"
     },
     "schedule": {
       "title": "Reminder Schedule",