Add multi-user features: i18n, payments, multi-model AI, focus areas

Replace single report type with composable analysis: depth levels
(basic/standard/full) + focus area multi-select (psychology, business,
marketing, content, audience, sentiment). Multi-step inline keyboard
flow guides users through selection.

- i18n: English + Russian, auto-detect from Telegram, /lang override
- AI providers: Anthropic + OpenRouter via AIClient abstraction
- Telegram Stars payments with per-depth pricing and free trial
- SQLite (aiosqlite) for users, analyses, payments tracking
- User middleware for auto-registration and language detection
- Report persistence: save .md locally, offer file download
- New commands: /features, /prices, /lang
- Composable prompt system: depth modifiers + focus area fragments

.env.example

@@ -4,3 +4,11 @@ TELEGRAM_API_HASH=
 TELEGRAM_PHONE=
 ANTHROPIC_API_KEY=
 CLAUDE_MODEL=claude-opus-4-6
+OPENROUTER_API_KEY=
+AVAILABLE_MODELS=claude-haiku-4-5,anthropic/claude-3.5-sonnet
+PRICE_BASIC=50
+PRICE_STANDARD=100
+PRICE_FULL=200
+FREE_ANALYSES=1
+DB_PATH=/app/data/bot.db
+REPORTS_DIR=/app/data/reports