feat(notification-service): replace Teams with Telegram notifications

Replace Microsoft Teams webhook integration with Telegram Bot API.
Remove Teams-specific models (MessageCard, Section, Fact) and service.
Add TelegramNotificationService using TELEGRAM_BOT_TOKEN and TELEGRAM_CHAT_ID
environment variables.

Assisted-by: Claude:claude-sonnet-4-6

notification_service/pom.xml

@@ -15,7 +15,7 @@
   <artifactId>notification-service</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>notification-service</name>
-  <description>Air quality alert notifications via Microsoft Teams</description>
+  <description>Air quality alert notifications via Telegram</description>
 
   <properties>
     <java.version>17</java.version>
@@ -32,6 +32,12 @@
       <optional>true</optional>
     </dependency>
 
+    <dependency>
+      <groupId>me.paulschwarz</groupId>
+      <artifactId>spring-dotenv</artifactId>
+      <version>4.0.0</version>
+    </dependency>
+
     <dependency>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-test</artifactId>