[Feature] TUI: Add action ribbon for better discoverability

[xodapi]

The TUI currently has powerful features (like trends on key \5, account switching on \Tab, help on ?), but they are practically invisible to a new user unless they've read the documentation carefully.

Tasks:

• Add a persistent bottom ribbon (footer) in the TUI indicating available hotkeys: ? help | 5 trends | Tab account | q quit.
• When the screen is empty/no trends are loaded, show a hint inside the main panel to press the relevant key.

[xodapi]

🤖 Начинаю выполнение. Агент: Factory Droid

[xodapi]

✅ PR готов: #39