Play sound-pack notifications for client actions

Adds TeamSpeak-format sound packs: a folder of waves plus a settings.ini
mapping actions to play()/say() entries, with ${clientType} and friends
resolved per event. Packs are found in the client's own sound folder, an
installed TS3 client and a folder of the user's choosing, so the official
packs work unchanged.

Each action can be switched off or marked important; important actions are
the only ones still played while the speakers are muted, as in TS3. The new
Notifications options page lists them by category, greys out what the active
pack has no sound for, and previews on double-click.

Sounds are decoded, resampled and mixed onto a single playback line that is
only open while something plays, so overlapping events never fight over the
device.

Fires the events from the protocol layer, following TeamSpeak's own
distinctions: reason ids separate switched/moved/kicked/banned/timed out,
and visibility decides appears/disappears/stays.

Also fixes a ts3j trap in the process: a field an event never carried reads
back as an empty string, so the existing "e.get(x) != null" checks were
always true. That made a partial clientupdate (someone muting) announce a
stopped recording, and it let a nickname-only update reset another client's
mute/away flags and talk power, or a channel edit blank the channel name.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ts3-client/README.md

@@ -80,6 +80,19 @@ frontend supplies its own UI and audio backend while reusing `core` unchanged.
 - **Status bar** shows the server name, user count and live ping.
 - Change your nickname, mute/deafen from the toolbar.
 
+### Notification sounds
+- **Sound packs** in TeamSpeak's own format: a folder of waves plus a `settings.ini`
+  mapping actions (`CONNECTION_CONNECTED`, `CLIENT_MOVED_TO_CURRENT_CHANNEL_STAYS`, …)
+  to `play("file.wav")` entries, with `${clientType}`/`${channelname}`/… placeholders
+  resolved per event. Packs are picked up from `~/.ts3jclient/sound`, an installed
+  TeamSpeak 3 client (`$TS3_CLIENT_DIR` or the usual install paths) and a folder of
+  your choosing, so the official packs work unchanged.
+- **Per-action configuration** (Options → Notifications): switch any action's sound
+  off, and mark actions as **important** (shown in bold, as in TS3) — important
+  actions are the only ones still played while the speakers are muted.
+- Sounds are mixed onto one playback line, so overlapping events never fight over
+  the device; pack volume is separate from the voice volume.
+
 ## Requirements
 - Java 26+ (developed/tested on Temurin 26)
 - The native Opus library on the system:
@@ -120,6 +133,13 @@ core/   com.ts3client
 │   ├── VoiceOutput          voice-packet playback sink
 │   ├── OpusParameters       live-tunable encoder settings
 │   └── SpeechDetector       feature-based speech-probability VAD (Automatic/Hybrid)
+├── sound
+│   ├── SoundEvent           catalogue of actions (TeamSpeak's own event ids)
+│   ├── SoundPack            a pack folder + its settings.ini mapping
+│   ├── SoundPacks           discovery of installed packs
+│   ├── NotificationSettings per-action enabled / important flags
+│   ├── SoundNotifier        decides what is heard (pack + config + mute state)
+│   └── SoundPlayer          platform hook for rendering a sound
 └── net
     ├── TeamspeakConnection  ties socket + audio backend + model, translates events
     ├── ServerModel          thread-safe channel/client state
@@ -132,6 +152,7 @@ desktop/  com.ts3client.audio.desktop
 ├── AudioDevices             device enumeration + line opening (48 kHz/16-bit)
 ├── JavaSoundVoiceInput      capture + VAD/PTT gating + Opus encode
 ├── JavaSoundVoiceOutput     per-client Opus decode + playback + mixing
+├── WavSoundPlayer           sound-pack playback: decode, resample and mix on one line
 └── JavaSoundAudioBackend    wires the above into the core AudioBackend
 
 swing/  com.ts3client
@@ -143,6 +164,7 @@ swing/  com.ts3client
     ├── InfoPanel            channel description / client group + details view
     ├── ChatPanel            chat log + input
     ├── SettingsDialog       audio + VAD options with live meter
+    ├── NotificationsPanel   sound pack + per-action sound/important configuration
     ├── ConnectDialog        connect form
     ├── BookmarksDialog      manage saved servers
     ├── IdentitiesDialog     manage identities (new/import/export/improve)