docs(changelog): add v1.20.0 entry

[ErickXavier]

Summary

• Added [1.20.0] - 2026-07-17 entry to CHANGELOG.md documenting the SSE directive feature (Added section with full attribute API breakdown), SSE-related fixes, and E2E test fixes
• Updated Unreleased compare link to point to v1.20.0...HEAD
• Aligned stale package-lock.json root version from 1.16.1 to 1.20.0 (2 fields only, no dependency churn)

[ErickXavier]

APPROVED — QA GATE (T9 / NOJS-279)

Verified:

• CHANGELOG [1.20.0] entry follows the repo's Keep a Changelog conventions exactly (inline compare link v1.19.0...v1.20.0, em-dash date 2026-07-17, intro narrative + ### Added/### Fixed sections matching the [1.19.0] house style; [Unreleased] link advanced to v1.20.0...HEAD).
• Every claim in the entry is TRUE against git log v1.19.0..feat/NOJS-270 and merged PRs #284–#290. No invented features. The only unmapped commits are internal bench chores, correctly omitted.
• package-lock.json diff touches ONLY the two root version fields (1.16.1 → 1.20.0, lines 3 and 9), now consistent with package.json and src/index.js (both 1.20.0). No dependency churn.
• Single conventional commit (docs(changelog): add v1.20.0 entry), author Erick Xavier, no AI attribution.
• /code-review pipeline (8 finder angles + verification): 1 confirmed finding, non-blocking (below). All other candidates refuted.

Non-blocking (wording, fix at leisure): the bullet says "validate sse-limit is a positive integer", but src/directives/sse.js:62-65 accepts 0 (treated as no-cap) and rejects only negative/non-numeric values — the code's own warning says "non-negative integer". Suggest changing the bullet to "non-negative integer".