Add 2026 French blockchain research note and update README

[Thedy09]

Motivation

• The repository is a blockchain learning/portfolio and needed a professional research publication to showcase research work and make it discoverable from the README.
• The research brief aims to present an evidence-based, practitioner-grade synthesis on stablecoins, Layer 2 scaling, tokenization of real-world assets, interoperability, and operational compliance for 2026.

Description

• Add essay-reflection/2026-blockchain-research-note-fr.md, a French-language research brief (~298 lines) with executive summary, methodology, analytical findings, strategic synthesis, recommendations, and references.
• Update README.md to reflect actual folder names (Capstone Project./, Certificates/, essay-reflection/, NANODEGREE/) and add a "Featured publication" entry linking the new note for visibility.
• All changes are documentation-only and do not modify code or runtime behavior.
• A PR message describing the addition and the README update was prepared for review.

Testing

• Ran git diff --check to detect whitespace/format problems and found no issues.
• Ran a verification script (python - <<'PY' ...) that confirmed the files exist and reported README.md: lines=71 and essay-reflection/2026-blockchain-research-note-fr.md: lines=298.
• Inspected file contents with nl -ba and spot-checked headers and sections to ensure the new note and README entries render and reference correctly.

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Codex Task