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>

.gitignore

@@ -20,13 +20,27 @@ build/
 
 # OS files
 .DS_Store
+Thumbs.db
+
+# IDE
+.vscode/
+.idea/
 
 # Streamlit
 .streamlit/
 **/.streamlit/
 
-# Lock files (optional, if not needed)
-uv.lock
+# Jupyter
+.ipynb_checkpoints/
+**/.ipynb_checkpoints/
 
-# Data files
+# Credentials & config with secrets
+*.cfg
+*.env
+.env
+
+# Large / binary data files
 *.csv
+*.zip
+*.sas7bdat
+*.parquet