tools(pc): audiodebug.ps1 audio-probe driver; gitignore run artifacts

audiodebug.ps1 drives the D202/D204 audio probes (health monitor,
GE_AUDIOTRACE/GE_AUDIODUMP, soundIndex histogram, -AB before/after runs —
how D204 was measured); companion to debug.ps1 (crashes). README table row
added. .gitignore: scratchpad/ + root-level audiodump/audiotrace/mixertrace
artifacts.

.gitignore

@@ -150,6 +150,12 @@ run_*.log
 d6*.log
 ge007.crash.log
 
+# agent scratch space + audio probe artifacts (regenerable dumps/traces)
+scratchpad/
+/audiodump.raw
+/audiotrace.log
+/mixertrace.log
+
 # Claude Code local state / agent worktrees
 .claude/