Fix open in agent mode context menu prompt

[caohai]

Pull Request Template – vscode-mssql

Description

Refactor the "Open in Agent Mode" context menu command to use JSON-formatted prompts instead of comma-delimited strings. This fixes:

• Ambiguity when server names contain commas (e.g., localhost,1433)
• Undefined values appearing in prompts by omitting empty/undefined fields

Most models didn't have issue with the old prompt but less performant models would not be able to recover / call list connections.

Before:

After:

Code Changes Checklist

• New or updated unit tests added
• All existing tests pass (npm run test)
• Code follows contributing guidelines
• Telemetry/logging updated if relevant
• No regressions or UX breakage

Reviewers: Please read our reviewer guidelines

[github-actions]

PR Changes

Category	Target Branch	PR Branch	Difference
vscode-mssql VSIX	5285 KB	5285 KB	⚪ 0 KB ( 0% )
sql-database-projects VSIX	5668 KB	5668 KB	⚪ 0 KB ( 0% )
data-workspace VSIX	null KB	532 KB	⚪ 532 KB ( 0% )

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.93%. Comparing base (2339af6) to head (eed82f7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20838      +/-   ##
==========================================
+ Coverage   65.91%   65.93%   +0.01%     
==========================================
  Files         210      210              
  Lines       19997    20004       +7     
  Branches     2600     2602       +2     
==========================================
+ Hits        13182    13189       +7     
  Misses       6718     6718              
  Partials       97       97              

Files with missing lines	Coverage Δ
extensions/mssql/src/controllers/mainController.ts	17.27% <100.00%> (+0.07%)	⬆️
extensions/mssql/src/copilot/tools/toolsUtils.ts	100.00% <100.00%> (ø)

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