5d35d75d

By: Michael Lynch <git@mtlynch.io>

Move Tinybeans conversion into the tinybeans package

Add tinybeans.Convert so callers can turn a parsed Tinybeans export into
Little Moments-native metadata without reimplementing the mapping logic.
This keeps the conversion boundary with the Tinybeans types while leaving
reactions work out of scope.

Update the import-from-tinybeans command to consume the new package API and
add unit tests for successful conversion and missing thumbnail failures.