Add mandatory commenting quality gate checklist (post_c72ee7a7)

[GVCUTV]

Motivation

• Introduce a mandatory closure checklist to enforce comment and inline-documentation quality and traceability for reviews after baseline c72ee7a7.

Description

• Add docs/commenting_quality_gate_post_c72ee7a7.md containing baseline/target and inventory placeholders, strict file-level pass/fail criteria (intent clarity, simple English, correctness, no stale/misleading comments), a spot-check matrix for backend/frontend/SQL/tests, a final PASS/FAIL decision template with blockers and open comment debt tracking, and an explicit presentation-readiness (speed/clarity) statement.

Testing

• No runtime tests were required for this documentation-only change, and the new file was validated locally by printing its contents with nl/sed and confirming the file is present in the working tree.

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Codex Task