feat: add bsky_post.py and Jenkinsfile for weekly Dijous post

- New standalone script `bsky_post.py` to post text + optional image
  or video to a Bluesky PDS instance. Supports --image, --video (mutually
  exclusive), --alt, --lang, --service, --username, --password flags.
  Reuses the same login-with-backoff pattern as rss2bsky and the Twitter bot.

- New Jenkinsfile that triggers every Thursday at 07:15 (cron: 15 7 * * 4),
  reads credentials from Jenkins secret text entries, and runs bsky_post.py
  with the configured image and Catalan language tag.

jenkins/dijous

@@ -0,0 +1,42 @@
+pipeline {
+    agent any
+
+    triggers {
+        // Every Thursday at 07:15
+        cron('15 7 * * 4')
+    }
+
+    environment {
+        BSKY_HANDLE          = credentials('BSKY_GROMENAWARE_HANDLE')
+        BSKY_APP_PASSWORD    = credentials('BSKY_GROMENAWARE_APP_PASSWORD')
+    }
+
+    options {
+        timeout(time: 10, unit: 'MINUTES')
+        buildDiscarder(logRotator(numToKeepStr: '30'))
+    }
+
+    stages {
+        stage('Post Dijous') {
+            steps {
+                sh """
+                    python3 bsky_post.py "Dijous!!!!" \\
+                        --username "\$BSKY_HANDLE" \\
+                        --password "\$BSKY_APP_PASSWORD" \\
+                        --image thursday.jpg \\
+                        --alt "Dijous!" \\
+                        --lang ca
+                """
+            }
+        }
+    }
+
+    post {
+        success {
+            echo '✅ Dijous post published successfully.'
+        }
+        failure {
+            echo '❌ Dijous post failed.'
+        }
+    }
+}