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/03-cloud-data-warehouse/dwh.cfg.example

@@ -0,0 +1,29 @@
+[AWS]
+KEY=YOUR_AWS_ACCESS_KEY_ID
+SECRET=YOUR_AWS_SECRET_ACCESS_KEY
+
+[CLUSTER]
+HOST=your-cluster.region.redshift.amazonaws.com
+DB_NAME=dev
+DB_USER=awsuser
+DB_PASSWORD=your_password
+DB_PORT=5439
+
+[IAM_ROLE]
+ARN=arn:aws:iam::YOUR_ACCOUNT_ID:role/myRedshiftRole
+
+[S3]
+LOG_DATA='s3://udacity-dend/log_data'
+LOG_JSONPATH='s3://udacity-dend/log_json_path.json'
+SONG_DATA='s3://udacity-dend/song_data'
+
+[DWH]
+DWH_CLUSTER_TYPE=multi-node
+DWH_NUM_NODES=1
+DWH_NODE_TYPE=dc2.large
+DWH_CLUSTER_IDENTIFIER=redshift-cluster-1
+DWH_DB=dev
+DWH_DB_USER=awsuser
+DWH_DB_PASSWORD=your_password
+DWH_PORT=5439
+DWH_IAM_ROLE_NAME=myRedshiftRole