docs: Cherry-pick PR #15719: Add v6.8.0 and v6.6.1 changelog entries to dev

[Copilot]

PR #15719 updated the VS Code extension changelog for the release/6.8 branch but was not synchronized to dev. This cherry-pick applies those changes.

Changes

• packages/vscode-extension/CHANGELOG.md
  • Added 6.8.0 (Apr 17, 2026) entry covering:
    • New features: DA + MCP CLI scaffolding, broker-based CLI auth, Azure AI Foundry C# template
    • Enhancements: manifest schema v1.25→v1.26, CLI template aliases, DA OpenAPI UX, metadata refresh, MCP gateway alignment
    • Bug fixes: DA MCP schema, Python template wiring, keytar crash, Linux PATH separators, MCP regressions, macOS playground, Teams SDK 2.0.7 compat, security dependency updates, CLI auth variable naming
  • Added 6.6.1 (Mar 26, 2026) hotfix entry for MCP tools parameter retrieval fix

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.32%. Comparing base (3014084) to head (138c4fb).
⚠️ Report is 5 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev   #15801   +/-   ##
=======================================
  Coverage   93.32%   93.32%           
=======================================
  Files         587      587           
  Lines       37120    37120           
  Branches     6772     6793   +21     
=======================================
  Hits        34641    34641           
  Misses       1835     1835           
  Partials      644      644           

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