feat: Tauri backend commands + wikipedia rewrite + github PR review pack

GUI integration
  - crates/jarvis-gui/src/tauri_commands/backends.rs — 5 new Tauri commands:
      get_active_backends()  -> {tts, llm, llm_model, profile}
      set_llm_backend(name)  -> swap LLM hot, persists to DB
      set_tts_backend(name)  -> persist choice (effective on jarvis-app restart)
      llm_reset_context()    -> clear conversation history
      llm_get_last_reply()   -> last assistant message or null
  - Registered in main.rs invoke_handler. Svelte side can now read active
    backend + swap from a settings page / footer without env-var gymnastics.

Wikipedia pack rewritten (resources/commands/wikipedia/)
  - Old `wiki/wiki.lua` (104 lines, hand-rolled Groq HTTP + inline SAPI PS) deleted.
  - Replacement `wikipedia/summary.lua` (87 lines):
    * REST summary endpoint (cleaner than opensearch+summary chain).
    * Russian first, English fallback with LLM translation.
    * Pure LLM fallback if Wikipedia has no article.
    * Uses jarvis.cmd.{ok,error,not_found} + jarvis.llm + jarvis.speak (no
      inline PowerShell SAPI). Phrases kept compatible with old pack.

GitHub PR voice review (resources/commands/github_pr/, 3 commands)
  - "текущий репо bossiara13/J.A.R.V.I.S-rust"  → github.set_repo
    Persists repo via jarvis.memory.
  - "какие пиары" / "открытые пиары"            → github.list_prs
    Calls `gh pr list --json number,title,author,createdAt --limit 10`.
    Parses count + first 3 titles by regex from JSON.
  - "разбери последний пиар" / "что в pr"       → github.summarize_pr
    `gh pr view N --json title,body,additions,deletions,changedFiles,author`,
    sends to LLM with "senior reviewer" system prompt, speaks 3-5 sentence
    review focusing on changes, risks, merge-readiness.
  - Requires gh CLI installed and `gh auth login` done.

Tests: 52/52 jarvis-core unit tests pass (Wikipedia pack TOML/script auto-checked).
Build: cargo build --release -p jarvis-app -p jarvis-gui green.

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

@@ -0,0 +1,81 @@
+//! Tauri commands for backend introspection + hot-swap. Used by the GUI
+//! footer to display the active LLM/TTS and let the user change them.
+//!
+//! Note: `get_active_backends` doesn't initialise the LLM — if the user
+//! never spoke to it, `llm_backend` may be "none" until first chat. That's
+//! the trade-off for avoiding cold-start latency in the GUI.
+
+use serde::Serialize;
+
+use jarvis_core::llm;
+use jarvis_core::tts;
+
+#[derive(Serialize)]
+pub struct ActiveBackends {
+    pub tts: String,
+    pub llm: String,
+    pub llm_model: Option<String>,
+    pub profile: String,
+}
+
+#[tauri::command]
+pub fn get_active_backends() -> ActiveBackends {
+    let llm_model = llm::current().map(|c| c.model().to_string());
+    ActiveBackends {
+        tts: tts::backend().name().to_string(),
+        llm: llm::current_backend_name().to_string(),
+        llm_model,
+        profile: jarvis_core::profiles::active_name(),
+    }
+}
+
+/// Hot-swap the LLM backend. Accepts "groq"/"ollama"/"cloud"/"local"/...
+/// Returns the new backend name on success, Err with reason on failure.
+#[tauri::command]
+pub fn set_llm_backend(name: String) -> Result<String, String> {
+    let backend = llm::parse_backend(&name)
+        .ok_or_else(|| format!("unknown backend: '{}'", name))?;
+    // Ensure global is initialised first (so swap can read DB-persisted choice).
+    if llm::current().is_none() {
+        let _ = llm::init_global();
+    }
+    llm::swap_to(backend)
+        .map(|n| n.to_string())
+        .map_err(|e| e.to_string())
+}
+
+/// Set TTS backend. Persists to settings DB. Effective on next jarvis-app start
+/// (TTS backend is OnceCell, can't hot-swap mid-process).
+#[tauri::command]
+pub fn set_tts_backend(name: String) -> Result<String, String> {
+    let normalized = match name.trim().to_lowercase().as_str() {
+        "" | "auto" => "".to_string(),
+        "sapi" | "piper" | "silero" => name.to_lowercase(),
+        other => return Err(format!("unknown TTS backend: '{}'", other)),
+    };
+
+    if let Some(db) = jarvis_core::DB.get() {
+        let snapshot = {
+            let mut s = db.write();
+            s.tts_backend = normalized.clone();
+            s.clone()
+        };
+        jarvis_core::db::save_settings(&snapshot)
+            .map_err(|e| format!("failed to persist: {}", e))?;
+        Ok(if normalized.is_empty() { "auto".into() } else { normalized })
+    } else {
+        Err("settings DB not initialised".into())
+    }
+}
+
+/// Reset conversation context (clears LLM history turns, keeps system prompt).
+#[tauri::command]
+pub fn llm_reset_context() {
+    llm::history_clear();
+}
+
+/// Return the most recent assistant message text (for "Repeat" button in GUI).
+#[tauri::command]
+pub fn llm_get_last_reply() -> Option<String> {
+    llm::history_last_assistant()
+}