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/helpers/sql_queries.py

@@ -0,0 +1,42 @@
+class SqlQueries:
+    songplay_table_insert = ("""
+        SELECT
+                md5(events.sessionid || events.start_time) songplay_id,
+                events.start_time, 
+                events.userid, 
+                events.level, 
+                songs.song_id, 
+                songs.artist_id, 
+                events.sessionid, 
+                events.location, 
+                events.useragent
+                FROM (SELECT TIMESTAMP 'epoch' + ts/1000 * interval '1 second' AS start_time, *
+            FROM staging_events
+            WHERE page='NextSong') events
+            LEFT JOIN staging_songs songs
+            ON events.song = songs.title
+                AND events.artist = songs.artist_name
+                AND events.length = songs.duration
+    """)
+
+    user_table_insert = ("""
+        SELECT distinct userid, firstname, lastname, gender, level
+        FROM staging_events
+        WHERE page='NextSong'
+    """)
+
+    song_table_insert = ("""
+        SELECT distinct song_id, title, artist_id, year, duration
+        FROM staging_songs
+    """)
+
+    artist_table_insert = ("""
+        SELECT distinct artist_id, artist_name, artist_location, artist_latitude, artist_longitude
+        FROM staging_songs
+    """)
+
+    time_table_insert = ("""
+        SELECT start_time, extract(hour from start_time), extract(day from start_time), extract(week from start_time), 
+               extract(month from start_time), extract(year from start_time), extract(dayofweek from start_time)
+        FROM songplays
+    """)