Puppeteer's ElementHandle.uploadFile and Playwright's setInputFiles drive
an <input type=file> through CDP DOM.setFileInputFiles, which obscura
rejected as an unknown method, so any upload flow failed (issue #359).
Implement it: resolve the node, read each local file, and hand the bytes
(base64) to the JS layer, which builds real File objects (backed by the
bytes, so page code can read them via FileReader or upload them via
fetch/FormData) and fires input+change like a genuine selection. The file
input exposes a FileList via .files, and .value reads C:\fakepath\<name>
to match Chrome.
Fixes#359.
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