feat: add scoreboard with player names, per-category leaderboards, and themed tables

Add player_name column to games (migration included), with regex-based
validation and anti-abuse sanitization. New /scoreboard page shows recent
games from localStorage, popular categories with play counts, and top-10
per-category leaderboards sorted by completion time. Also includes
two-click reverse word matching, base URL prefix support for reverse-proxy
hosting, BasePageHandler refactoring, themed table CSS for all 5 themes,
and comprehensive test coverage for player names and scoreboard API.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

alembic/versions/3a2aa8e15433_add_player_name_to_games.py

@@ -0,0 +1,40 @@
+"""add player_name to games
+
+Revision ID: 3a2aa8e15433
+Revises: 71016fe57b9d
+Create Date: 2026-05-07 02:32:19.229401
+
+"""
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision: str = "3a2aa8e15433"
+down_revision: Union[str, Sequence[str], None] = "71016fe57b9d"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column(
+        "games",
+        sa.Column(
+            "player_name",
+            sa.String(length=20),
+            server_default="Anonymous",
+            nullable=False,
+        ),
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_column("games", "player_name")
+    # ### end Alembic commands ###