`I'm` is not among the spellcheck suggestions for `im`

People often type in all lowercase and without punctuation for efficiency or chatty style, etc. If you want to use Harper to correct these into standard orthography it misses that "im" means "I'm", the contraction for "I am".

Reproduce the spellcheck suggestion behavior for lowercase `im` in Harper and compare it with the expected suggestions shown in the issue screenshots. Trace the Rust spellchecking or suggestion entry point responsible for contraction handling, then verify that `I'm` appears as a suggestion without breaking related correction cases.

Written by the indexing model from the issue text.