feat: [sc-125395] Add QOSS survey toast coach mark to Sphinx themes (XST + PST)

[derekokelly-rgb]

Story details: https://app.shortcut.com/xanaduai/story/125395

[github-actions]

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[Copilot]

Pull request overview

Adds an optional, dismissible “toast” coach mark to the Xanadu Sphinx theme, intended to show a short prompt near the top of the page after a configurable delay (and only once per browser session).

Changes:

• Introduces new theme options (coach_mark_enabled, coach_mark_toast) and documents their usage.
• Adds a new coach_mark.html template included from layout.html, plus JS logic to show/dismiss/track the toast.
• Adds CSS for the toast layout, styling, and entrance animation (with reduced-motion support).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
xanadu_sphinx_theme/theme.conf	Adds new theme configuration knobs for enabling and configuring the coach mark toast.
xanadu_sphinx_theme/static/xanadu.css_t	Adds styling and animations for the CoachMark toast component.
xanadu_sphinx_theme/layout.html	Includes the new coach mark template and adds JS to position/show/dismiss/track the toast.
xanadu_sphinx_theme/coach_mark.html	Adds the toast HTML template rendered conditionally based on theme options.
README.rst	Documents the new configuration options and expected data shape.

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