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/02-cassandra-modeling/README.md

@@ -0,0 +1,45 @@
+# Data Modeling with Apache Cassandra
+
+**Udacity Data Engineering Nanodegree — Project 2**
+
+## Overview
+
+Model and query a NoSQL database using **Apache Cassandra** for the fictional Sparkify music streaming service. Unlike relational databases, Cassandra requires a _query-first_ design approach: each table is purpose-built to answer one specific analytical question.
+
+## Dataset
+
+Raw event data is sourced from CSV log files (`event_data/2018-11-*.csv`) representing daily user activity. These files are pre-processed and merged into a single consolidated dataset (`event_datafile_new.csv`) before loading into Cassandra.
+
+**Sample fields:** `artist`, `firstName`, `gender`, `itemInSession`, `lastName`, `length`, `level`, `location`, `sessionId`, `song`, `userId`
+
+## Schema Design
+
+Three tables are modeled to answer three specific queries:
+
+| Table | Partition Key | Clustering Columns | Answers |
+|---|---|---|---|
+| `session_songs` | `sessionId` | `itemInSession` | What song was played in a given session and item? |
+| `user_session_songs` | `userId`, `sessionId` | `itemInSession` | What songs did a user listen to in a session? |
+| `song_listeners` | `song` | `userId` | Who listened to a specific song? |
+
+## Key Concepts
+
+- **Query-first modeling** — schema designed around queries, not entities
+- **Denormalization** — data is duplicated across tables to enable fast reads
+- **Partition keys** — determine data distribution across nodes
+- **Clustering columns** — control sort order within a partition
+- **`cassandra-driver`** — Python client for Cassandra
+
+## How to Run
+
+1. Install dependencies:
+   ```bash
+   pip install cassandra-driver pandas
+   ```
+
+2. Open and run the notebook:
+   ```bash
+   jupyter notebook "Project_1B_ Project_Template.ipynb"
+   ```
+
+The notebook walks through preprocessing the CSV data, creating Cassandra tables, inserting records, and running validation queries.