Feature/app-icon

[MacBuchi]

Changes

UI — modern header

• Fixed-height dark header bar matching the BG_Header gradient palette (#090c15) sits above the existing toolbar
• Logo.png displayed at 76 x 53 px on the left side
• App title bold, light-blue tint (#daeef8)
• Subtitle muted cyan (#4a7a92)
• 2 px accent line (#1e5f7a) between header and toolbar for visual separation
• Window default size bumped 1060x560 to 1060x628, minsize 900x420 to 900x490

Asset loading (_BUNDLE_DIR / _load_ctk_image)

• _BUNDLE_DIR resolves to sys._MEIPASS inside a frozen .app, and to the repo root when running from source
• _load_ctk_image(filename, size) opens a PNG from Pics/ as a CTkImage, returning None gracefully on failure

PyInstaller spec

• Pics/*.png are now collected into the bundle so the header logo is available in .app / Windows build

Tests — tests/test_app_smoke.py

• test_app_starts_and_stays_alive: launches MultiChannelWavMixer.py as a subprocess, asserts it is still alive after 6 seconds, then terminates it
• On failure, stderr is captured and surfaced in the pytest output
• Skipped on Linux (no native display) — the pytest CI job runs on macos-latest so it always executes there