feat: LLM auto-fallback + codegen pack + OCR pack

LLM auto-fallback (jarvis-app/src/app.rs + jarvis-core/src/config.rs):
- When neither intent classifier nor levenshtein finds a command match,
  route the utterance straight to the LLM instead of just playing the
  "not found" sound. Triggers ("скажи X", "answer Y") still work and
  take precedence — they short-circuit before command lookup.
- Two new config knobs:
    LLM_AUTO_FALLBACK = true        — master toggle
    LLM_AUTO_FALLBACK_MIN_CHARS = 4 — suppress for very short utterances
                                       so background noise doesn't burn
                                       Groq quota
- Requires GROQ_TOKEN; if absent, behaviour is unchanged (play_not_found).

codegen/ command pack:
- Phrases: "напиши код X", "сгенерируй скрипт Y", "write code Z", etc.
- Strips the trigger from the recognized phrase, sends what remains to
  Groq with a strict system prompt ("return ONLY code, no fences, no
  commentary") at temperature 0.2.
- Parses the JSON content, unescapes \n / \" / \\ / \t, strips any
  remaining ```lang ... ``` fences, drops the result into the clipboard
  via jarvis.system.clipboard.set.
- Notifies a 120-char preview + plays ok-sound. Works for any language
  the model handles (Python by default if unspecified).
- GROQ_TOKEN / GROQ_MODEL / GROQ_BASE_URL read from env at call time —
  same envvars the voice-loop fallback already uses.

ocr/ command pack:
- Phrases: "прочитай экран", "что на экране", "read screen", etc.
- Captures the primary screen via System.Windows.Forms + System.Drawing
  to a temp PNG, then shells to tesseract.exe (-l rus+eng for ru/ua,
  -l eng for en).
- Resolves Tesseract by PATH first, then C:\Program Files\Tesseract-OCR
  and the x86 install dir; if none works the user gets a friendly
  "winget install UB-Mannheim.TesseractOCR" hint in a notification.
- Recognized text goes to clipboard + a 200-char preview notification.

All three features are portable (env-var resolution, no hardcoded user
paths). Command-pack total is now 11. cargo test -p jarvis-core --lib
commands::tests passes 3/3.

resources/commands/ocr/command.toml

@@ -0,0 +1,26 @@
+[[commands]]
+id = "read_screen"
+type = "lua"
+script = "read_screen.lua"
+sandbox = "full"
+timeout = 30000
+
+[commands.phrases]
+ru = [
+    "прочитай экран",
+    "что на экране",
+    "распознай текст с экрана",
+    "что написано на экране",
+    "сними текст с экрана",
+]
+en = [
+    "read screen",
+    "what is on screen",
+    "ocr screen",
+    "extract text from screen",
+]
+ua = [
+    "прочитай екран",
+    "що на екрані",
+    "розпізнай текст з екрана",
+]