fix(gui): suppress blank progress log chunks

[SpencerJung]

Closes #33

Summary

• Treat standalone carriage returns, newlines, and whitespace-only stdout chunks as non-log output.
• Keep PROG:<N> parsing in the GUI-free helper module so the filtering behavior stays unit-testable.
• Suppress empty progress redraw artifacts in the textbox while preserving real log lines.

Issue Evidence

• Issue [Bug] Console multiple "empty enters" and blank lines #33 was reopened after a prior fix because the console still filled with blank rows while progress updates were running.
• Root cause: main.py:add_log_raw filtered PROG: directives, but still inserted standalone \r, \n, and whitespace-only chunks into the textbox.
• The GUI now ignores those chunks before writing to the console.

Verification

• python tests/test_progress_line.py — passed.
• python -m py_compile main.py utils/progress_line.py tests/test_progress_line.py — passed.
• git diff --check — passed.
• LSP diagnostics for utils/progress_line.py — clean.
• main.py LSP shows environment-level missing dependency warnings (customtkinter, PIL, dotenv, spotipy) in this shell, but no change-specific parser/integration errors.

Community Rules Review

• Focused PR for a single issue/concern.
• Split into two atomic commits: parser/tests, then GUI integration.
• No unauthorized version bump.
• No workflow/tracker/profile files included in the target repo diff.