* Security hardening for Try Cosmos DB connection string flow
- Validate connection string format via parseConnectionString before accepting postMessage
- Restrict localhost:12900 in allowedHostedExplorerEndpoints to development builds only
- Export App component for testability with null-check on render target
- Add 12 unit tests covering origin validation, format validation, and message handling
* Fix HostedExplorer test mock types for compile
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Co-authored-by: Asier Isayas <aisayas@microsoft.com>
asier-isayas