Upgrade image-size to official patched release

[VdustR]

Resolve the remaining image-size security dependency gap by upgrading the documentation dependency and Docusaurus MDX loader's compatible transitive resolution from locally patched 2.0.2 to official 2.0.4. Remove the local patch only after verifying equivalent protection against all five malformed-input fixtures.

• Unpatched 2.0.2 hangs in isolated ICNS, HEIF, and JXL cases; patched 2.0.2 and official 2.0.4 terminate with errors.
• Retain the five security regressions with a two-second subprocess timeout so a synchronous loop cannot hang CI. Add dimension checks for valid inputs in all three affected parsers.
• Preserve all unrelated lockfile versions. Node >=18 required by image-size 2.0.4 is within this repository's Node >=20.19 support.

Validation on Node 26.10.0 / pnpm 10.34.5:

• Frozen installation; 13 tests passed.
• Root and documentation type checks; package and documentation production builds.
• git diff --check; full diff independently inspected.
• pnpm audit has no image-size finding; seven unrelated fast-uri / brace-expansion advisories remain outside this change.

After merge, verify the main-push Pages deployment, production page and Dependabot's natural fixed state. No version tag or npm release is required for this documentation dependency update.

Closes #6

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