* fix: remove escapeMarkdownSyntaxTokens from terminal command labels
Fixes#303844
The command text in ChatTerminalThinkingCollapsibleWrapper was being
escaped with escapeMarkdownSyntaxTokens(), which adds backslashes before
chars like - * # etc. This is unnecessary because the text is always
rendered inside markdown code spans or via .textContent, both of which
treat content as literal.
Also adds a component fixture for the terminal collapsible wrapper to
enable visual regression testing of command label rendering.
* fix: use DOM nodes instead of MarkdownString for sandbox command labels
Addresses review feedback: commands containing backticks (common in
PowerShell) would break the inline-code markdown spans. Now both
sandbox and non-sandbox paths use text nodes + <code> elements with
.textContent, which is always safe for arbitrary command text.
Also adds fixture cases for backtick-containing commands to catch
this class of issue.
* fix: remove colons from fixture names to fix CI artifact paths
* add screenshot baselines for terminal collapsible fixtures
