Add self-hosted usage analytics: pageview tracking + admin stats dashboard

Records pageviews (path, referrer, browser/OS/device, IP, GeoIP country) via
a POST /api/track beacon into a new PageView table, and exposes aggregated
daily/breakdown stats behind a token-gated GET /api/admin/stats endpoint with
brute-force lockout. Frontend gets a /admin dashboard (charts + breakdown
tables) built on recharts, with a switchable per-day pageviews chart.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

db/models.py

@@ -1,6 +1,6 @@
-"""ORM modely: Player, Game, Guess.
+"""ORM modely: Player, Game, Guess, PageView.
 
-Zamerne minimalne (3 tabulky). `won` sa neuklada -- vyplyva z `points > 0`
+`won` sa neuklada -- vyplyva z `points > 0`
 (trafeny tip = 10 + tip, inak 0; pozri Round.get_points_summary v bridzik.py).
 """
 
@@ -83,3 +83,22 @@ class Guess(Base):
     round_number: Mapped[int] = mapped_column(Integer)
     guess: Mapped[int] = mapped_column(Integer)
     points: Mapped[int] = mapped_column(Integer)
+
+
+class PageView(Base):
+    """Jedna navsteva stranky (pre /track). Bez schema migracii -- create_all only."""
+
+    __tablename__ = "page_views"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    path: Mapped[str] = mapped_column(String(200))
+    referrer: Mapped[str] = mapped_column(String(300), default="")
+    user_agent: Mapped[str] = mapped_column(String(300), default="")
+    browser: Mapped[str] = mapped_column(String(40), default="")
+    os: Mapped[str] = mapped_column(String(40), default="")
+    device_type: Mapped[str] = mapped_column(String(20), default="")  # mobile/tablet/pc/bot
+    ip: Mapped[str] = mapped_column(String(45), default="")  # surova IP (IPv4/IPv6), "" ak nezname
+    country: Mapped[str] = mapped_column(String(2), default="")  # ISO kod z GeoIP, "" ak nerozlusene
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime, server_default=func.now()
+    )