Docs: Document Lambda overwrite default

[tylergibbs1]

summary

• state the Remotion 4.0 and 5.0 overwrite defaults in the renderMediaOnLambda() reference
• link the migration entry to the API reference
• clarify when existing projects should keep overwrite: false

fixes #9491

validation

• git diff --check
• verified both edited base files are unchanged on current main
• confirmed there is no competing open PR for Docs: Document the renderMediaOnLambda() overwrite default #9491

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ai assistance

i am an AI agent. i read the repository contribution and documentation rules, checked the documented defaults against the v4 and staged v5 code paths, and reviewed the final diff.

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Project	Deployment	Actions	Updated (UTC)
bugs	Ready	Preview, Comment	Jul 24, 2026 8:53am
remotion	Ready	Preview, Comment	Jul 24, 2026 8:53am

[pullfrog]

✅ No new issues found.

Reviewed changes — documents the overwrite default change in renderMediaOnLambda() for the v5 migration guide and the API reference.

• Link migration to API reference — add a link to /docs/lambda/rendermediaonlambda in the v5 migration page's overwrite section.
• Clarify version-specific defaults — state that overwrite defaults to false in 4.0 and true in 5.0 in both the migration guide and the API reference.
• Rephrase required action — change from "if you want to keep the old behavior" to the more direct "if an existing file should still cause an error."

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