docs: fix typos in readme and spec files

[itsvedantkumar]

Four spelling mistakes in documentation:

• separte -> separate (binary/README.md)
• delimeter -> delimiter (core/diff/test-examples/README.md)
• overriden -> overridden (extensions/cli/spec/permissions.md)
• instaed -> instead (sync/src/README.md)

Found with codespell, then each one read in context so nothing inside a code block or an identifier was touched. Docs only -- no code, no build input

I left two categories alone on purpose: anything under core/vendor/ (third-party code, not ours to correct) & the CHANGELOG.md files (a historical record of what was written at the time)

AI usage disclosure: I used Claude to run the spell check & prepare the diff. I checked every change myself and I am responsible for what is here

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