feat(patterns): add audio domain — PipeWire/ALSA xrun and quantum patterns

Six new patterns covering the PipeWire + ALSA audio failure modes that
surface as crackling/stuttering on Linux desktops:

- pipewire_overflow: protocol-pulse OVERFLOW channel messages (confirmed
  present in Muninn journal — dozens per incident)
- pipewire_underrun: pw.node/spa.alsa underrun messages
- alsa_xrun: ALSA-level xrun from kernel or ALSA lib (snd_pcm)
- pipewire_quantum_mismatch: sample-rate/quantum mismatch detection
- pipewire_node_error: PipeWire node failures (device unavailable)
- pipewire_jackdbus_missing: harmless JACK probe at INFO — suppresses
  false positives from daily PipeWire restarts

Also adds 'audio' as a valid domain value in the header comment.

Companion Robin knowledge doc:
  circuitforge-plans/robin/known-issues/pipewire-alsa-quantum-xrun.md

patterns/default.yaml

@@ -4,7 +4,7 @@
 #
 # domain: groups patterns into service health domains for triage-level summaries.
 # Valid domains: service_health | networking | auth | storage | memory |
-#                kernel | power | web_proxy | media | gpu
+#                kernel | power | web_proxy | media | gpu | audio
 #
 # Patterns are applied in order; multiple can match a single entry.
 
@@ -275,3 +275,41 @@ patterns:
     severity: ERROR
     domain: power
     description: Undervoltage event — instability risk, check PSU and cable connections
+
+  # ── Audio / PipeWire / ALSA ──────────────────────────────────────────────────
+
+  - name: pipewire_overflow
+    pattern: "(OVERFLOW channel|stream.*OVERFLOW|protocol.pulse.*OVERFLOW)"
+    severity: WARN
+    domain: audio
+    description: PipeWire-Pulse stream buffer overflow — client not draining audio fast enough; usually indicates a quantum/period-size mismatch or CPU scheduling issue
+
+  - name: pipewire_underrun
+    pattern: "(pw\\.node.*underrun|spa\\.alsa.*underrun|alsa.*underrun|UNDERRUN)"
+    severity: WARN
+    domain: audio
+    description: PipeWire/ALSA buffer underrun (xrun) — audio thread missed its deadline; increase quantum or period-size for the affected device
+
+  - name: alsa_xrun
+    pattern: "(ALSA.*[Xx][Rr][Uu][Nn]|alsa.*xrun|snd_pcm.*xrun|pcm.*underrun|pcm.*overrun)"
+    severity: WARN
+    domain: audio
+    description: ALSA xrun (hardware buffer overrun/underrun) — increase api.alsa.period-size via WirePlumber rule or raise clock.min-quantum
+
+  - name: pipewire_quantum_mismatch
+    pattern: "(quantum.*mismatch|rate.*mismatch|sample.rate.*mismatch|resampl.*fail|can.*t adapt quantum)"
+    severity: WARN
+    domain: audio
+    description: PipeWire quantum or sample-rate mismatch between nodes — check for mixed 44100/48000 streams; may need per-device WirePlumber rules
+
+  - name: pipewire_node_error
+    pattern: "(pw\\.node.*error|node.*ERROR|pipewire.*failed to set|spa\\.alsa.*error|alsa_sink.*error|alsa_source.*error)"
+    severity: ERROR
+    domain: audio
+    description: PipeWire node error — device may be unavailable or misconfigured
+
+  - name: pipewire_jackdbus_missing
+    pattern: "(jackdbus.*reply|jackaudio.*service.*not.*provided|org\\.jackaudio\\.service)"
+    severity: INFO
+    domain: audio
+    description: PipeWire JACK D-Bus probe — JACK not running; benign on non-JACK systems, fires once per PipeWire restart