feat: persist LLM/TTS backend choice + reset/repeat context + quick-search + diagnostics

Closes the UX hole I created in 5c72450: voice-swap to Ollama used to vanish
after restart. Plus P0.3 (long-standing roadmap item) and two new packs.

Persistent backend choice (crates/jarvis-core/src/db/structs.rs)
  - Settings struct gains llm_backend + tts_backend fields (both String,
    "" / "auto" = follow env/auto-detect).
  - set("llm_backend", "groq"|"ollama"|"auto") validates input.
  - llm::init_global() reads DB first, then JARVIS_LLM env, then auto-detect.
  - llm::swap_to() now persists the choice via db::save_settings.
  - Voice swap "переключись на локальный" now survives restart.

Shared conversation history (P0.3, crates/jarvis-core/src/llm/mod.rs)
  - HISTORY: Lazy<RwLock<Option<ConversationHistory>>> singleton.
  - Helpers: init_history, history_push_user, history_push_assistant,
    history_snapshot, history_clear, history_pop_last_user, history_last_assistant.
  - llm_fallback migrated off its own Mutex<History> — now reads/writes shared.
  - ConversationHistory gains last_assistant() method.

New Lua APIs
  - jarvis.llm_reset()        → clear conversation turns (keeps system prompt).
  - jarvis.llm_last_reply()   → string or nil (last assistant message text).
  - jarvis.health()           → debug table {tts_backend, llm_backend, llm_model,
                                  active_profile, memory_facts, scheduled_tasks,
                                  language, voice, microphone, vosk_model,
                                  noise_suppression}. No secrets included.

New voice packs
  - resources/commands/llm_context/   (P0.3)
    * "сбрось контекст" / "забудь разговор"     → llm.reset
    * "повтори последнее" / "повтори ответ"     → llm.repeat (uses last_assistant)
  - resources/commands/quick_search/   (imba P1 item)
    * "найди в гугле <X>" / "загугли <X>"
    * Uses DuckDuckGo Instant Answer API (api.duckduckgo.com, no key required).
      Pulls AbstractText or RelatedTopics into LLM prompt; falls back to pure
      LLM knowledge if DDG returns nothing useful. Speaks 2-4 sentence answer.
  - resources/commands/diagnostics/
    * "диагностика" / "доложи о себе" / "статус"
    * Reads jarvis.health() and speaks a one-line summary. Useful when
      debugging — user can read out their current state for a bug report.

Build: cargo build --release -p jarvis-app -p jarvis-gui green.
Tests: 52/52 jarvis-core unit tests pass.

resources/commands/quick_search/command.toml

@@ -0,0 +1,31 @@
+# Quick-search-read — answer questions using DuckDuckGo Instant Answer API + LLM.
+# No API key required. Falls back to pure LLM if web search returns nothing.
+
+[[commands]]
+id = "quick_search"
+type = "lua"
+script = "search.lua"
+sandbox = "full"
+timeout = 30000
+
+[commands.phrases]
+ru = [
+    "найди в гугле",
+    "найди в интернете",
+    "поищи в гугле",
+    "найди и расскажи",
+    "загугли",
+    "посмотри в гугле",
+    "поищи информацию",
+    "найди информацию о",
+]
+en = [
+    "google for",
+    "search for",
+    "find online",
+    "look up",
+]
+ua = [
+    "знайди в гуглі",
+    "погугли",
+]

resources/commands/quick_search/search.lua

@@ -0,0 +1,83 @@
+-- "Найди в гугле что такое квантовая запутанность"
+-- Uses DuckDuckGo's free Instant Answer API (api.duckduckgo.com). No key.
+-- The IA response often has a "Abstract" / "AbstractText" / "AbstractURL" set
+-- for well-known topics. We feed Abstract + RelatedTopics to the LLM for a
+-- spoken summary. Falls back to pure LLM knowledge if DDG returns nothing useful.
+
+local phrase = (jarvis.context.phrase or "")
+
+local query = jarvis.text.strip_trigger(phrase:lower(), {
+    "найди и расскажи",
+    "найди в гугле",
+    "найди в интернете",
+    "поищи в гугле",
+    "посмотри в гугле",
+    "загугли",
+    "поищи информацию о",
+    "поищи информацию",
+    "найди информацию о",
+    "google for",
+    "search for",
+    "find online",
+    "look up",
+    "знайди в гуглі",
+    "погугли",
+})
+query = query:gsub("^[%s,:%.]+", ""):gsub("%s+$", "")
+
+if query == "" then
+    return jarvis.cmd.error("Что искать?")
+end
+
+local function urlencode(s)
+    return (s:gsub("[^A-Za-z0-9%-_%.~]", function(c)
+        return string.format("%%%02X", string.byte(c))
+    end))
+end
+
+local url = "https://api.duckduckgo.com/?q=" .. urlencode(query)
+              .. "&format=json&no_html=1&skip_disambig=1"
+
+local data = jarvis.http.json(url)
+
+local context = ""
+if data then
+    if data.AbstractText and data.AbstractText ~= "" then
+        context = data.AbstractText
+        if data.AbstractURL and data.AbstractURL ~= "" then
+            context = context .. "\nИсточник: " .. data.AbstractURL
+        end
+    elseif data.RelatedTopics and #data.RelatedTopics > 0 then
+        local lines = {}
+        for i = 1, math.min(4, #data.RelatedTopics) do
+            local t = data.RelatedTopics[i]
+            if t.Text then table.insert(lines, t.Text) end
+        end
+        context = table.concat(lines, "\n")
+    end
+end
+
+local user_prompt
+if context ~= "" then
+    user_prompt = string.format(
+        "Вопрос пользователя: %s\n\nДанные из веб-поиска:\n%s\n\nОтветь на вопрос по-русски, кратко (2-4 предложения), используя данные. Если данных мало — добавь из своих знаний.",
+        query, context
+    )
+else
+    user_prompt = string.format(
+        "Вопрос пользователя: %s\n\nВеб-поиск ничего полезного не дал. Ответь по-русски кратко (2-4 предложения), используя свои знания. Если не уверен — скажи об этом.",
+        query
+    )
+end
+
+local answer = jarvis.llm({
+    { role = "system", content = "Ты — справочный помощник. Отвечай кратко и по делу, без вводных фраз." },
+    { role = "user", content = user_prompt }
+}, { max_tokens = 350, temperature = 0.3 })
+
+if not answer or answer == "" then
+    return jarvis.cmd.error("Не получилось получить ответ.")
+end
+
+jarvis.system.notify("Поиск: " .. query, answer:sub(1, 200))
+return jarvis.cmd.ok(answer)