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

bot/db/usage_repo.py

@@ -0,0 +1,46 @@
+import json
+
+from bot.db.engine import get_db
+
+
+async def record_analysis(
+    telegram_id: int,
+    channel: str,
+    depth: str,
+    focus_areas: list[str],
+    model_id: str,
+    stars_paid: int = 0,
+    report_path: str | None = None,
+) -> int:
+    db = await get_db()
+    cursor = await db.execute(
+        "INSERT INTO analyses (telegram_id, channel, depth, focus_areas, model_id, stars_paid, report_path) "
+        "VALUES (?, ?, ?, ?, ?, ?, ?)",
+        (telegram_id, channel, depth, json.dumps(focus_areas), model_id, stars_paid, report_path),
+    )
+    await db.commit()
+    return cursor.lastrowid
+
+
+async def update_report_path(analysis_id: int, report_path: str) -> None:
+    db = await get_db()
+    await db.execute(
+        "UPDATE analyses SET report_path = ? WHERE id = ?", (report_path, analysis_id)
+    )
+    await db.commit()
+
+
+async def record_payment(
+    telegram_id: int,
+    telegram_payment_id: str,
+    stars_amount: int,
+    analysis_id: int | None = None,
+) -> int:
+    db = await get_db()
+    cursor = await db.execute(
+        "INSERT INTO payments (telegram_id, telegram_payment_id, stars_amount, analysis_id) "
+        "VALUES (?, ?, ?, ?)",
+        (telegram_id, telegram_payment_id, stars_amount, analysis_id),
+    )
+    await db.commit()
+    return cursor.lastrowid