* fix(sdk): add prototype-pollution guard to migration config merge
mergeMigrationConfigValue and writeMigrationConfigPath had no
isBlockedObjectKey guard, allowing __proto__/constructor/prototype
keys from imported config files to trigger prototype pollution.
Add the same guard used by the sibling config-path writer
(setConfigValueAtPath/parseConfigPath) to reject blocked object
keys before they reach a bracket assignment.
Fixes#103059
* fix(sdk): harden migration config patches
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Co-authored-by: Peter Steinberger <steipete@gmail.com>