[docs][P3] CONTRIBUTING.md: changelog statement contradicts existing CHANGELOG.md

[FabioLeitao]

docs token | thin slice | Composer 2

What to fix

CONTRIBUTING.md "Release history and changelog" states: "A separate CHANGELOG file in the repo is not required."

But CHANGELOG.md exists at the root, is tracked by git, and is actively maintained (Unreleased section + entries back to v1.6.7).

Fix (Option A — preferred)

Replace the stale sentence in CONTRIBUTING.md (EN) and CONTRIBUTING.pt_BR.md (pt-BR):

# Current (wrong)
A separate CHANGELOG file in the repo is not required; use docs/releases/ and tags for "where we are" and progress.

# Replace with
CHANGELOG.md at the repo root is the human-readable summary of user-facing changes per release. For detailed release checklists and Docker publish commands, see docs/releases/ (one file per version).

1. Verify CHANGELOG.md is tracked and non-empty: git ls-files CHANGELOG.md
2. Update CONTRIBUTING.md section "Release history and changelog"
3. Mirror in CONTRIBUTING.pt_BR.md
4. Gate: .\scripts\lint-only.ps1
5. Commit: docs(contributing): correct changelog statement — CHANGELOG.md is maintained

Out of scope

Do not delete or restructure files. Documentation fix only.