Add search messages and schema updates

[corinac123]

Added app function to search messages.
Update schema with some nit renames.

[gemini-code-assist]

Code Review

This pull request refactors the chat application's app functions by renaming the message sending function to sendMessage (returning a simple string), updating ContactSearchResult with more descriptive fields, and introducing a new searchMessages function along with its corresponding data models and tests. The review feedback suggests validating against empty queries in searchMessages to prevent performance and privacy issues, querying messages concurrently rather than sequentially, and optimizing searchRecipients by applying take(maxCount) before mapping the elements when the query is blank.

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