chore: update CHANGELOG for Q2 2026 (v2.3.0)

[danbaruka]

Description

This PR adds a [2.3.0] - 2026-06-04 entry to CHANGELOG.md documenting DevEx Working Group work from Q2 2026 (Apr–Jun).

• Problem: The changelog stopped at 2.2.2 (Q1 2026, Mar 2026) and did not reflect Q2 session docs, guides, milestone reports, or related fixes.
• Purpose: Give the community a single, versioned record of Q2 deliverables under Keep a Changelog / SemVer conventions.

Related Issue

N/A

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactor (improves code structure or readability without changing functionality)
• Other (please describe):

Changes Made

• Updated CHANGELOG.md with release [2.3.0] - 2026-06-04
• Added: Q2 2026 WG Sessions 14–18 (offchain/SDK walkthrough, dApp architecture, UI ↔ smart contracts, default dev environment, Cardano MCP server); Yaci DevKit guide; Blaze + Yaci Store integration guide; cardano-node emulator tutorial; Developer Advocates Cohort 2 impact report; Q2 milestone docs (pain points, language-inclusive onboarding)
• Changed: Q2 session meet link/time; advanced README and dApp architecture indexing notes
• Fixed: Dependabot security alerts; DevEx Sessions button overlap on desktop
• Documentation: Developer Pathway Mermaid improvements; Open Clinic Update readme #2; Session 7 updates
• Chore: Docusaurus 3.10.0; GitHub Actions and website dependency bumps

Checklist

• My code follows the project's coding style and guidelines.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation (if applicable).
• My changes generate no new warnings or errors.
• I have added tests that prove my fix is effective or that my feature works.
• I have checked for merge conflicts.
• I have rebased my branch onto the latest main or master branch.