feat: hot-swap LLM backend + media keys + codebase Q&A + scheduler cancel-by-text + TTS pre-warm

Single biggest user-facing change: you can now switch local↔cloud LLM by voice
without restarting. Plus four new packs and a perf nudge.

Shared LLM global (crates/jarvis-core/src/llm/mod.rs)
  - GLOBAL: Lazy<RwLock<Option<Arc<LlmClient>>>>. Single source of truth.
  - init_global() / current() / swap_to(LlmBackend) / current_backend_name() / parse_backend(str).
  - llm_fallback + llm_router migrated: they no longer own a separate LlmClient,
    they read from the global on each request. Hot-swap is now LIVE — change
    backend, next chat call uses the new one.
  - parse_backend accepts both english and russian aliases:
      "groq"/"cloud"/"облако"/"клауд"        → Groq
      "ollama"/"local"/"локал"/"локальный"  → Ollama

Voice + Lua LLM switcher (resources/commands/llm_switch/, 3 commands)
  - "переключись на локальный" / "перейди на оллама"  → swap to Ollama
  - "переключись на облако" / "используй грок"        → swap to Groq
  - "какой у тебя мозг" / "облако или локально"       → status query

  Underlying Lua API (registered globally):
    jarvis.llm({messages}, opts)   -- as before, now uses global client
    jarvis.llm_status()            -> "groq" | "ollama" | "none"
    jarvis.llm_switch(name)        -> name on success, nil on failure

Media keys pack (resources/commands/media_keys/, 4 commands)
  - "пауза" / "плей"           → VK_MEDIA_PLAY_PAUSE
  - "следующий трек"           → VK_MEDIA_NEXT_TRACK
  - "предыдущий трек"          → VK_MEDIA_PREV_TRACK
  - "стоп музыка"              → VK_MEDIA_STOP
  - Helper _media.ps1 uses user32.keybd_event (P/Invoke through Add-Type).
  - Works with anything that listens to global media keys: Spotify, Yandex Music,
    YouTube (focused tab), Foobar2000, Winamp, etc. No OAuth, no API keys.

Codebase Q&A pack (resources/commands/codebase_qa/, 3 commands)
  - "укажи проект <path>"             → stores path in jarvis.memory under codebase.root
  - "какой проект сейчас"             → speaks current path
  - "что делает функция X" / "найди в коде Y" / "объясни код"
    → walks the folder (depth 3, 30 files cap, 4KB per file, 50KB total),
      filters by source extensions (rs/py/ts/lua/go/...), feeds digest to LLM
      with a "senior reviewer" system prompt, speaks 3-5 sentence answer.

Scheduler cancel-by-text (crates/jarvis-core/src/scheduler.rs)
  - new pub fn find_by_text(query, limit) -> Vec<ScheduledTask>
  - new pub fn remove_by_text(query) -> usize (count removed)
  - new pure helper find_by_text_in(tasks, query, limit) for tests
  - Lua: jarvis.scheduler.{find_by_text, remove_by_text}
  - Voice: "отмени напоминание про воду" / "удали задачу про разминку"
  - 3 new unit tests (52 total in jarvis-core).

TTS pre-warm (crates/jarvis-app/src/main.rs)
  - Call jarvis_core::tts::backend() once on startup so the first speak()
    doesn't pay Piper binary discovery + voice loading cost. Cuts first-speak
    latency by ~150-300ms depending on backend.

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

resources/commands/llm_switch/command.toml

@@ -0,0 +1,62 @@
+# Switch between local (Ollama) and cloud (Groq) LLM at runtime.
+
+[[commands]]
+id = "llm.switch.local"
+type = "lua"
+script = "switch.lua"
+sandbox = "standard"
+timeout = 3000
+
+[commands.phrases]
+ru = [
+    "переключись на локальный",
+    "переключись на локальный мозг",
+    "включи локальный режим",
+    "перейди на локальный",
+    "используй локальный",
+    "перейди на оллама",
+    "используй оллама",
+]
+en = ["switch to local", "use local llm", "use ollama"]
+ua = ["перейди на локальний", "використовуй локальний"]
+
+
+[[commands]]
+id = "llm.switch.cloud"
+type = "lua"
+script = "switch.lua"
+sandbox = "standard"
+timeout = 3000
+
+[commands.phrases]
+ru = [
+    "переключись на облако",
+    "переключись на облачный",
+    "переключись на грок",
+    "переключись на гроку",
+    "используй облако",
+    "используй грок",
+    "перейди на облако",
+]
+en = ["switch to cloud", "use cloud llm", "use groq"]
+ua = ["перейди на хмару", "використовуй хмару"]
+
+
+[[commands]]
+id = "llm.status"
+type = "lua"
+script = "status.lua"
+sandbox = "minimal"
+timeout = 2000
+
+[commands.phrases]
+ru = [
+    "какой у тебя мозг",
+    "какой ллм",
+    "какой у тебя llm",
+    "облако или локально",
+    "ты сейчас где работаешь",
+    "что за модель",
+]
+en = ["which llm", "are you local or cloud", "what model"]
+ua = ["який ллм", "хмара чи локально"]

resources/commands/llm_switch/status.lua

@@ -0,0 +1,8 @@
+local backend = jarvis.llm_status()
+if backend == "groq" then
+    return jarvis.cmd.ok("Сейчас работаю на облаке.")
+elseif backend == "ollama" then
+    return jarvis.cmd.ok("Сейчас работаю локально.")
+else
+    return jarvis.cmd.not_found("LLM не настроен.")
+end

resources/commands/llm_switch/switch.lua

@@ -0,0 +1,22 @@
+-- Map command id → backend name (see command.toml).
+local cmd_id = jarvis.context.command_id or ""
+local target
+if cmd_id:match("local") then
+    target = "ollama"
+elseif cmd_id:match("cloud") then
+    target = "groq"
+else
+    return jarvis.cmd.error("Не понял на что переключать.")
+end
+
+local result = jarvis.llm_switch(target)
+if not result then
+    local human = (target == "ollama") and "локальный" or "облачный"
+    return jarvis.cmd.error("Не получилось переключиться на " .. human .. ".")
+end
+
+if result == "groq" then
+    return jarvis.cmd.ok("Переключился на облачный мозг.")
+else
+    return jarvis.cmd.ok("Переключился на локальный мозг.")
+end