Add certificate validation and PGP/MIME encryption; rename to pro.thinhha.mailsender

- validation: CertificateValidator checks revocation, expiry, matching
  user ID, a valid communications encryption subkey and the algorithm
  policy; uses the earlier expiry when PGPainless and Bouncy Castle disagree
- crypto: PgpEncryptor (ASCII armor, hidden recipients for Bcc)
- mime: PgpMimeEncryptor builds RFC 3156 multipart/encrypted from the
  whole CRLF-canonical inner entity, keeping envelope headers in the clear
- autoconfigure: validator and encryptor beans
- demo: encrypts when a valid key is found, plaintext otherwise
- rename groupId and Java packages to pro.thinhha.mailsender

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G71TQ5jDETVwdUJxGAwaiT

mailsender-pgp-core/pom.xml

@@ -5,7 +5,7 @@
     <modelVersion>4.0.0</modelVersion>
 
     <parent>
-        <groupId>io.github.sneakybugmaster.mailsender</groupId>
+        <groupId>pro.thinhha.mailsender</groupId>
         <artifactId>mailsender-parent</artifactId>
         <version>0.1.0-SNAPSHOT</version>
     </parent>
@@ -30,6 +30,11 @@
             <groupId>org.slf4j</groupId>
             <artifactId>slf4j-api</artifactId>
         </dependency>
+        <dependency>
+            <!-- Jakarta Mail API + implementation (same as spring-boot-starter-mail) -->
+            <groupId>org.eclipse.angus</groupId>
+            <artifactId>angus-mail</artifactId>
+        </dependency>
 
         <dependency>
             <groupId>org.junit.jupiter</groupId>