Fix WebSocket crash from oversized client messages

[MisterGC]

Fixes #155

Drogon's default 128 KB WebSocket client message size limit caused std::terminate when clients sent large tile requests.

• Raise Drogon's client WS message size limit from 128 KB to 10 MB
• Add try-catch around sendControlMessage() to handle send failures on dying connections
• Add try-catch around onTileLayer() to catch exceptions from tile serialization/streaming
• Add try-catch around handleNewMessage() since Drogon calls it with no exception protection

TODO

• Decide whether to also limit request size at the protocol level to avoid depending on Drogon's frame-size limit. Options include: capping tile count per request, chunking large requests into multiple messages, or moving bulk request payloads to HTTP POST and keeping the WebSocket as a small control channel only. This would also require client-side changes in erdblick.

[sonarqubecloud]

Quality Gate failed

Failed conditions
16.3% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud

[github-actions]

Package	Line Rate	Branch Rate	Health
libs.geojsonsource.include.geojsonsource	100%	50%	✔
libs.geojsonsource.src	67%	34%	➖
libs.gridsource.include.gridsource	0%	0%	❌
libs.gridsource.src	0%	0%	❌
libs.http-datasource.src	57%	31%	➖
libs.http-service.include.mapget.http-service	100%	100%	✔
libs.http-service.src	61%	25%	➖
libs.logging.include.mapget	7%	3%	❌
libs.model.include.mapget.model	51%	29%	➖
libs.model.src	68%	38%	➖
libs.service.include.mapget.service	58%	50%	➖
libs.service.src	71%	35%	➖
Summary	60% (6770 / 11205)	31% (6875 / 22261)	➖

Minimum allowed line rate is 50%