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/plugins/operators/data_quality.py

@@ -0,0 +1,22 @@
+from airflow.hooks.postgres_hook import PostgresHook
+from airflow.models import BaseOperator
+from airflow.utils.decorators import apply_defaults
+
+class DataQualityOperator(BaseOperator):
+
+    ui_color = '#89DA59'
+
+    @apply_defaults
+    def __init__(self,
+                 # Define your operators params (with defaults) here
+                 # Example:
+                 # conn_id = your-connection-name
+                 *args, **kwargs):
+
+        super(DataQualityOperator, self).__init__(*args, **kwargs)
+        # Map params here
+        # Example:
+        # self.conn_id = conn_id
+
+    def execute(self, context):
+        self.log.info('DataQualityOperator not implemented yet')