chore: ignore .vscode/ editor scaffolding

[VAsHachiRoku]

Summary

Launching this repository from Developer Control Tower left .vscode/ showing as an
untracked directory, so the working tree was never clean after a launch.

Two different files were involved, with different origins:

• .vscode/tasks.json is written by Developer Control Tower itself when it starts a
  Copilot CLI session for this folder. The tool already keeps this out of version
  control by appending /.vscode/tasks.json to .git/info/exclude, which is
  deliberate so it never edits a tracked .gitignore in someone else's repository.
• .vscode/launch.json is scaffolded by the VS Code C# extension and was not covered
  by anything. It was the only genuinely untracked file; git status --short collapses
  the directory to ?? .vscode/, which made both look untracked.

Neither file is shared configuration. launch.json is a console-debug configuration
pointed at ControlTower.Tests rather than the WPF desktop app, and the generated task
carries per-user session flags. This adds .vscode/ to .gitignore alongside the
existing .vs/ and .idea/ entries, so editor and tool scaffolding is treated the same
way regardless of which editor produced it.

Behavior and risk

User-visible behavior

• No runtime, UI, or packaging change. This is a single line in .gitignore.
• The working tree stays clean after launching this repository from the app.

Scope

• Nothing was tracked under .vscode/ before this change (git ls-files .vscode is
  empty), so no file is being un-tracked and no contributor loses a committed config.
• The tool's .git/info/exclude mechanism is left untouched. It remains the correct
  behavior for repositories the tool does not own; this change only covers the
  editor-generated remainder in this repository.
• A future shared config under .vscode/ can still be added deliberately with
  git add -f.

Security impact

• None directly, though it removes a standing chance of committing the generated task,
  which records personal launch flags such as the agent name and session options.
• No secrets, machine paths, or portfolio state are added. .gitignore already ignores
  user and machine state for this tool.

Rollback

• Delete the line. Any .vscode/ files on disk are untouched either way.

Validation

• Targeted tests added or updated
• dotnet test DeveloperControlTower.sln -c Release
• No secrets, private assets, portfolio data, or machine paths added
• GitHub Actions, if changed, use full immutable SHAs

No tests were added and the suite was not run locally: this change touches no compiled
code, only .gitignore. CI runs the full build and test suite on this pull request as a
required status check, which covers the no-regression case.

Validation performed was on the ignore behavior itself:

Command	Result
git check-ignore -v .vscode/launch.json	.gitignore:4:.vscode/ — now ignored
git check-ignore -v .vscode/tasks.json	.gitignore:4:.vscode/ — now ignored
git status --porcelain --untracked-files=all	Empty — working tree fully clean
git ls-files .vscode	Empty — nothing previously tracked, nothing un-tracked

No workflow files were changed.