chore: bump version to 18.0.1 and add changelog

[boehlerlukas]

First half of the usual release pair (chore: bump version … → vX): package.json, package-lock.json, CHANGELOG.md only.

18.0.1 ships what is on master since 18.0.0:

• Cap the replay buffer by size and resend oversized reports without it (Gleap #147738) #148 — replay buffer capped by size (~10 MB), 413'd reports resent without the replay (Gleap #147738)
• feat: maintain verified sessions for protected conversation files #147 — opt-in authenticated conversation files

Not included, as in previous releases: the v18.0.1 build commit (build/, published/18.0.1/, published/latest/), npm publish, npm run deploy, and the version table in gleap-api-docs/introduction.mdx.

Merge #149 (comment-only) first if it should be part of 18.0.1.

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