feat: Wave 3 — plugin loader + Flet GUI (parity with Rust fork)

Plugin loader (mirrors Rust #29):
- plugins_store.py walks %APPDATA%\com.priler.jarvis\plugins\<name>\
  for commands.yaml fragments and merges them into VA_CMD_LIST at
  startup. Same schema as the project root commands.yaml. Per-pack
  `disabled` flag file skips a pack without deletion. Built-in ids
  win conflicts so a malicious pack can't silently override
  open_browser. 9 unit tests (parity with the Rust tests).
- main.py: plugin merge runs after the root yaml load; logs the
  number of extra commands picked up.

Flet GUI (#27 — first parity with the Rust Tauri GUI):
- New gui/ package: __main__.py launches via `python -m gui` (or
  gui.bat). app.py routes between 7 pages (Главная / Команды /
  Макросы / Расписание / Память / Плагины / Настройки) via
  NavigationRail; dark theme matching the Tauri look.
- gui/services.py centralises every store-module call the pages
  share — single place to swap implementations later.
- One file per page in gui/pages/, all expose `build(page)` and use
  the same card layout idiom. Pages mirror the Tauri ones feature-
  for-feature: home (status + counters + launcher), commands
  (filterable list of all VA_CMD_LIST entries), macros (list +
  delete + recording banner), scheduler (list + remove), memory
  (add/forget/search), plugins (toggle/open folder), settings
  (profile + LLM hot-swap).
- requirements.txt: flet>=0.85 (optional; assistant runs without).
- 3 smoke tests verify imports + build callables; skip cleanly when
  Flet isn't installed.

README: documents both the GUI and the plugin layout in user-facing
terms. Tests: 42 → 54 (+9 plugins +3 GUI smoke).

gui/__init__.py

@@ -0,0 +1,19 @@
+"""Python Flet GUI — Russian-language desktop UI mirroring the Rust Tauri GUI.
+
+Entry point: `python -m gui` (see `__main__.py`).
+
+Layout:
+    gui/__init__.py    # this docstring
+    gui/__main__.py    # `python -m gui` entry
+    gui/app.py         # routing, layout, theme
+    gui/pages/         # one file per page (home, commands, macros, ...)
+    gui/services.py    # thin sync wrappers around store modules
+
+Design notes:
+- Each page is a function `build(page: ft.Page) -> ft.Control` returning a
+  composable view. This keeps state per-page lazy and lets the user navigate
+  without prematurely loading everything.
+- The GUI does not start the assistant; it only manipulates state files and
+  hot-launches `main.py` in a subprocess (mirroring how the Rust GUI starts
+  jarvis-app.exe via tray).
+"""