feat: Wave 3 — plugin system + custom wake-word trainer

#29 Plugin system:
- New jarvis-core::plugins module: discovers user packs in
  %APPDATA%\com.priler.jarvis\plugins\<name>\command.toml so authors can
  ship voice commands without rebuilding. Sandbox capped at "standard" —
  plugins cannot escalate to "full" (which would expose `os`). Disabled
  via a `disabled` flag file. Malformed packs warn and skip; never poison
  the rest of the list. 8 unit tests.
- commands::parse_commands() merges plugins into the loaded list.
- New /plugins GUI page with enable/disable switches, error reporting,
  "Open folder" button. Tauri commands plugins_list / plugins_set_enabled
  / plugins_open_folder. Header gets a "Плагины" button. i18n keys added
  for ru/en/ua.

#8 Custom wake-word trainer wizard:
- New jarvis-core::wake_trainer module: opens its own pv_recorder
  instance, records N short PCM clips, WAV-encodes them in memory, then
  calls rustpotter's WakewordRef::new_from_sample_buffers to train and
  persist a .rpw model under %APPDATA%/com.priler.jarvis/wake_words/.
  Keepsake WAVs are also dumped for retraining later. Sanitises names to
  block path traversal. 5 unit tests.
- Settings gain `custom_wake_word: String`; listener/rustpotter.rs now
  loads the user's selected model first and always falls back to the
  bundled default so the assistant keeps working even if the custom
  file is missing.
- New /wake-trainer GUI page: stepper UI for record-sample → train,
  shows recorded count, threshold slider, refuses to start while
  jarvis-app is running (mic exclusivity). Lists existing trained
  models with size + delete button.
- 8 Tauri commands wired through (status/defaults/start/record_sample/
  finish/cancel/list_models/delete_model).

Tests: 115 → 128 (+8 plugins +5 wake_trainer). Release builds green for
all three binaries (jarvis-app / jarvis-cli / jarvis-gui).

crates/jarvis-gui/src/tauri_commands/plugins.rs

@@ -0,0 +1,47 @@
+//! Tauri commands for the plugin system. GUI uses these to render
+//! `/plugins` page: list installed plugins, toggle enabled state, reveal the
+//! plugins folder in Explorer, and open the docs page.
+
+use serde::Serialize;
+use std::path::PathBuf;
+
+#[derive(Serialize)]
+pub struct PluginEntry {
+    pub name: String,
+    pub path: String,
+    pub enabled: bool,
+    pub command_count: usize,
+    pub error: Option<String>,
+}
+
+#[tauri::command]
+pub fn plugins_list() -> Vec<PluginEntry> {
+    jarvis_core::plugins::list()
+        .into_iter()
+        .map(|p| PluginEntry {
+            name: p.name,
+            path: p.path.display().to_string(),
+            enabled: p.enabled,
+            command_count: p.command_count,
+            error: p.error,
+        })
+        .collect()
+}
+
+#[tauri::command]
+pub fn plugins_set_enabled(name: String, enabled: bool) -> Result<(), String> {
+    jarvis_core::plugins::set_enabled(&name, enabled)
+}
+
+#[tauri::command]
+pub fn plugins_open_folder() -> Result<String, String> {
+    let dir: PathBuf = jarvis_core::plugins::plugins_dir()?;
+    // Open the folder in Explorer (Windows-only — fall back to printing path).
+    #[cfg(target_os = "windows")]
+    {
+        let _ = std::process::Command::new("explorer.exe")
+            .arg(&dir)
+            .spawn();
+    }
+    Ok(dir.display().to_string())
+}

crates/jarvis-gui/src/tauri_commands/wake_trainer.rs

@@ -0,0 +1,50 @@
+//! Tauri commands for the wake-word trainer wizard. The GUI drives the
+//! whole flow over these — see `frontend/src/routes/wake-trainer/index.svelte`.
+//!
+//! Key safety note: pv_recorder claims the mic exclusively, so the wizard
+//! refuses to enter recording mode while jarvis-app.exe is running. The frontend
+//! also checks this beforehand and prompts the user to stop the daemon.
+
+use jarvis_core::wake_trainer::{
+    self, TrainedModelInfo, TrainerStatus, DEFAULT_SAMPLE_SECONDS, DEFAULT_TARGET_SAMPLES,
+};
+
+#[tauri::command]
+pub fn wake_trainer_status() -> TrainerStatus {
+    wake_trainer::status()
+}
+
+#[tauri::command]
+pub fn wake_trainer_defaults() -> (f32, u8) {
+    (DEFAULT_SAMPLE_SECONDS, DEFAULT_TARGET_SAMPLES)
+}
+
+#[tauri::command]
+pub fn wake_trainer_start(name: String, target_samples: u8) -> Result<(), String> {
+    wake_trainer::start(&name, target_samples)
+}
+
+#[tauri::command]
+pub fn wake_trainer_record_sample(seconds: f32) -> Result<usize, String> {
+    wake_trainer::record_sample(seconds)
+}
+
+#[tauri::command]
+pub fn wake_trainer_finish(threshold: f32) -> Result<String, String> {
+    wake_trainer::finish(threshold).map(|p| p.display().to_string())
+}
+
+#[tauri::command]
+pub fn wake_trainer_cancel() {
+    wake_trainer::cancel()
+}
+
+#[tauri::command]
+pub fn wake_trainer_list_models() -> Vec<TrainedModelInfo> {
+    wake_trainer::list_models()
+}
+
+#[tauri::command]
+pub fn wake_trainer_delete_model(name: String) -> Result<(), String> {
+    wake_trainer::delete_model(&name)
+}