Separate player list visibility from position tracking

[jpenilla]

Player position tracking and sidebar player-list visibility currently share
configuration indirectly.

When player-tracker.enabled is false, position and tracker telemetry are
omitted, but player identity and world data remain in players.json so the
player can still appear in the sidebar. The frontend now handles that state
correctly as of aac1bd1.

Add separate per-world controls for position tracking and player-list
visibility.

Position tracking	Player list	Result
Enabled	Enabled	Full player data, map marker, and sidebar entry
Disabled	Enabled	Identity/world data and sidebar entry, without a marker
Enabled	Disabled	Full position data and map marker, without a sidebar entry
Disabled	Disabled	Player omitted from players.json

The sidebar player list is global:

• A player should appear in the list only when player-list visibility is
  enabled for that player's world.
• Players used only for map markers should not appear in the list or its
  current-player count.
• The entire Players section, including the Players (0/max) heading, should
  be hidden when player-list visibility is disabled for every enabled map
  world.
• If at least one enabled map world exposes its player list, the Players
  section should remain available.

Existing behavior should remain the default for compatibility. Exact
configuration names and layout can be decided during implementation.

This supersedes:

• Fully disable player list when player-tracker is disabled #59
• [Feature Request] #455

This does not change per-player /map hide and /map show behavior or the
meaning of the marker layer's default-hidden setting.