Sound options: per-channel preview samples (651bd1)

Card 651bd1 — Sound-Optionen: Test-Sample beim Ändern pro Kanal

All 5 channels were staged-only until 'Save & Update' — volume was tuned blind. Now a representative sample plays at the STAGED volume × staged master.

Implementation

• DrawSoundChanger — returns the slider interaction {Dragging, ToggleFlipped} as a 4th value; drawChangers is its only consumer (flag: backward-compatible).
• DrawSoundOptions — per-channel cached love.audio sources + FILE_ChannelState frame-state machine: Vol@DragStart captured on drag-begin, preview fires on release iff changed; toggle-click previews post-flip state.
• Samples: Master/Effects → Buildingplacement1.mp3; Music → first Music/*.mp3 via BastiFileSystem.dir (folder is build-level — nothing hardcoded, flag 1); Voice → CommenceExtraction.mp3 (own source — VoiceManager reads saved volume + owns in-flight files); Ambience → Ambience.wav.
• Guards: stop() before play() (retrigger); toggle-off stops in-flight sample; master-off skips all previews; stopAllPreviews() on Save & Update.
• Ambience standalone vars normalized through updateChannel (flag 6).

Verified: luajit per-file + lovec .syntaxchk 4056/0.