fix: rollback must restore AudioConfig period/rate + LATENCY_PROFILES

The profile change rollback only restored audio_sys.config.profile to
old_key, but my earlier fix had started syncing period/rate to AudioConfig
BEFORE start_jack(). This meant the rollback's start_jack() still used
the NEW period/rate (via latency_profile) because self.period was never
reverted — the same failing config was retried and failed again.

Fix: capture old_period, old_rate, and old LATENCY_PROFILES['custom']
entry before applying the new profile, then restore all of them in the
rollback path.

src/web/server.py

@@ -1674,6 +1674,10 @@ class WebServer:
                 return {"ok": True, "profile": effective_key, "restarted": False}
 
             # ── Apply new profile on the fly ─────────────────────────
+            # Capture old values for rollback
+            old_period = audio_sys.config.period
+            old_rate = audio_sys.config.rate
+            old_entry = LATENCY_PROFILES.get("custom")
             # Update AudioConfig — store named overrides inline in profile key
             audio_sys.config.profile = effective_key
 
@@ -1719,8 +1723,15 @@ class WebServer:
             ok = await loop.run_in_executor(None, partial(audio_sys.start_jack, timeout=15))
             audio_sys.config.auto_connect = saved_auto_connect
             if not ok:
-                # Rollback on failure
+                # Rollback on failure — restore AudioConfig fields too
                 audio_sys.config.profile = old_key
+                audio_sys.config.period = old_period
+                audio_sys.config.rate = old_rate
+                # Restore the old LATENCY_PROFILES entry
+                if old_entry is not None:
+                    LATENCY_PROFILES["custom"] = old_entry
+                elif "custom" in LATENCY_PROFILES:
+                    del LATENCY_PROFILES["custom"]
                 logger.warning("JACK restart failed — attempting rollback to %s", old_key)
                 ok = await loop.run_in_executor(None, partial(audio_sys.start_jack, timeout=15))
                 if jack_client: