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.

resources/commands/github_pr/list.lua

@@ -0,0 +1,39 @@
+local repo = jarvis.memory.recall("github.repo")
+if not repo or repo == "" then
+    return jarvis.cmd.not_found("Сначала укажите репозиторий: текущий репо owner/repo.")
+end
+
+local result = jarvis.system.exec(string.format(
+    'gh pr list --repo "%s" --state open --json number,title,author,createdAt --limit 10',
+    repo
+))
+if not result or not result.success then
+    local err = (result and result.stderr) or "gh CLI не доступен"
+    jarvis.log("warn", "gh failed: " .. err)
+    return jarvis.cmd.error("gh CLI не отвечает. Установите gh и выполните gh auth login.")
+end
+
+local stdout = result.stdout or ""
+if stdout:gsub("%s", "") == "" or stdout:gsub("%s", "") == "[]" then
+    return jarvis.cmd.ok("Открытых пиаров нет.")
+end
+
+-- Parse JSON via LLM (mlua doesn't ship a JSON parser by default).
+-- Alternatively count number entries with a regex.
+local _, count = stdout:gsub('"number"%s*:', "")
+if count == 0 then
+    return jarvis.cmd.ok("Открытых пиаров нет.")
+end
+
+-- Get titles
+local titles = {}
+for title in stdout:gmatch('"title"%s*:%s*"([^"]+)"') do
+    table.insert(titles, title)
+    if #titles >= 3 then break end
+end
+
+local line = string.format("%d открытых пиаров. ", count)
+if #titles > 0 then
+    line = line .. "Первые: " .. table.concat(titles, ". ") .. "."
+end
+return jarvis.cmd.ok(line)