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/__init__.py

@@ -0,0 +1,19 @@
+from __future__ import division, absolute_import, print_function
+
+from airflow.plugins_manager import AirflowPlugin
+
+import operators
+import helpers
+
+# Defining the plugin class
+class UdacityPlugin(AirflowPlugin):
+    name = "udacity_plugin"
+    operators = [
+        operators.StageToRedshiftOperator,
+        operators.LoadFactOperator,
+        operators.LoadDimensionOperator,
+        operators.DataQualityOperator
+    ]
+    helpers = [
+        helpers.SqlQueries
+    ]