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/06-immigration-capstone/dl.cfg.example

@@ -0,0 +1,10 @@
+[AWS]
+AWS_ACCESS_KEY_ID=YOUR_AWS_ACCESS_KEY_ID
+AWS_SECRET_ACCESS_KEY=YOUR_AWS_SECRET_ACCESS_KEY
+
+[IAM_ROLE]
+ARN=arn:aws:iam::YOUR_ACCOUNT_ID:role/myRedshiftRole
+
+[S3]
+SOURCE_S3_BUCKET=s3a://your-bucket/
+DEST_S3_BUCKET=s3a://your-bucket/