Update DropzoneJS library to the latest secure release (upgrade tool-chain dependencies)

Problem/Motivation

The DropzoneJS library located in libraries/dropzone/ is still built with an outdated JavaScript tool-chain that carries known CVEs:

• webpack 5.23.0 — CVE-2023-28154 (Critical)
• terser ≤ 5.6 — CVE-2022-25858 (High)
• postcss ≤ 8.2.6 — CVE-2021-23382 (High)
• loader-utils 1.4 / 2.0 — CVE-2022-37599 / 37603 (High)
• json5 ≤ 2.2.0 — CVE-2022-46175 (High)

These packages are build-time dependencies, so the runtime risk is not severe, but modernizing them removes security alerts and future-proofs the codebase.

Steps to reproduce

1. Inspect web/libraries/dropzone/yarn.lock.
2. Note the versions listed above.
3. Run any vulnerability scanner; the CVEs are flagged.

Proposed resolution

1. Bump DropzoneJS to the latest 6.x tag (currently 6.1.0).
2. Run yarn install && yarn build with:
   • webpack ≥ 5.76.0
   • terser ≥ 5.14.2
   • postcss ≥ 8.4.37
   • loader-utils ≥ 2.0.4
   • json5 ≥ 2.2.2
3. Commit the regenerated /dist assets and updated yarn.lock.

Remaining tasks

• Create a patch/MR updating package.json and yarn.lock.
• Re-build assets and commit the new /dist.
• Smoke-test drag-and-drop uploads (Media Library, entity browser).
• Tag a new 2.x release once verified.

User interface changes

None expected—the Dropzone widget should behave identically.

API changes

None.

Data model changes

None.