Remove in-game Squaremap/FactionMap background features, keep claim sync

[plan3t]

Motivation

• The in-game Squaremap tile background feature introduced a lot of UI/packet coupling and compile-time churn; the goal is to remove the background UI/metadata surface while preserving claim synchronization with Squaremap.

Description

• Removed the Squaremap tile background provider implementation and its client routing so the client no longer fetches or renders Squaremap tiles (deleted SquaremapTileBackgroundProvider and removed references to it in MapBackgroundProviders).
• Simplified client-side map background state to a minimal provider toggle (NONE / XAERO) and removed zoom/texture preferences and related UI hooks in FactionMapClientData and FactionMainScreen so background controls/status are no longer shown or used.
• Removed server config entries and server-side background metadata resolution related to the in-game Squaremap background by making FactionClaimMapPacket.resolveBackgroundMetadata(...) return none() and by deleting the squaremapUi* config options from FactionConfig.
• Kept the Squaremap bridge claim-sync functionality intact (SquaremapBridge.updateClaim / syncClaims) so Factions ↔ Squaremap marker synchronization remains available.

Testing

• Ran ./gradlew compileJava --no-daemon, which completed successfully and showed the codebase compiles after the removals.

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Codex Task