refactor: restructure monorepo for clean portfolio layout

- Move timesfm-forecast into apps/ directory
- Flatten Udacity portfolio projects from deep URL-encoded paths
  into data-engineering/01-XX numbered directories
- Remove old My-Data-Engineering-Portifolio/ parent directory
- Rewrite root README.md: professional overview with badges,
  project table, and repo structure diagram
- Create data-engineering/README.md with per-project descriptions
- Add README.md for 02-cassandra-modeling (was missing)
- Add README.md for 05-airflow-pipelines (was missing)
- Normalize capstone readme.md -> README.md
- Update .gitignore: add *.cfg, *.env, *.zip, *.sas7bdat,
  Jupyter checkpoints, IDE dirs; remove uv.lock exclusion
- Add dwh.cfg.example and dl.cfg.example credential templates
- Untrack real credential files (dwh.cfg, dl.cfg)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

data-engineering/05-airflow-pipelines/dags/udac_example_dag.py

@@ -0,0 +1,65 @@
+from datetime import datetime, timedelta
+import os
+from airflow import DAG
+from airflow.operators.dummy_operator import DummyOperator
+from airflow.operators import (StageToRedshiftOperator, LoadFactOperator,
+                                LoadDimensionOperator, DataQualityOperator)
+from helpers import SqlQueries
+
+# AWS_KEY = os.environ.get('AWS_KEY')
+# AWS_SECRET = os.environ.get('AWS_SECRET')
+
+default_args = {
+    'owner': 'udacity',
+    'start_date': datetime(2019, 1, 12),
+}
+
+dag = DAG('udac_example_dag',
+          default_args=default_args,
+          description='Load and transform data in Redshift with Airflow',
+          schedule_interval='0 * * * *'
+        )
+
+start_operator = DummyOperator(task_id='Begin_execution',  dag=dag)
+
+stage_events_to_redshift = StageToRedshiftOperator(
+    task_id='Stage_events',
+    dag=dag
+)
+
+stage_songs_to_redshift = StageToRedshiftOperator(
+    task_id='Stage_songs',
+    dag=dag
+)
+
+load_songplays_table = LoadFactOperator(
+    task_id='Load_songplays_fact_table',
+    dag=dag
+)
+
+load_user_dimension_table = LoadDimensionOperator(
+    task_id='Load_user_dim_table',
+    dag=dag
+)
+
+load_song_dimension_table = LoadDimensionOperator(
+    task_id='Load_song_dim_table',
+    dag=dag
+)
+
+load_artist_dimension_table = LoadDimensionOperator(
+    task_id='Load_artist_dim_table',
+    dag=dag
+)
+
+load_time_dimension_table = LoadDimensionOperator(
+    task_id='Load_time_dim_table',
+    dag=dag
+)
+
+run_quality_checks = DataQualityOperator(
+    task_id='Run_data_quality_checks',
+    dag=dag
+)
+
+end_operator = DummyOperator(task_id='Stop_execution',  dag=dag)