docs: align README, roadmap, framework wording, and AI prompt docs

[cwinland]

Summary

This PR completes the current v4 public-doc cleanup set and keeps the staged AI-doc work in the same change.

What changed

• refreshes the root README as the top-level FastMoq evaluation page
• aligns the public roadmap with the live public backlog and moves detailed generator planning into its own roadmap companion page
• removes xUnit-specific product positioning while keeping example-only and framework-specific references where they are still useful
• expands the feature-parity page into a clearer comparison aid
• adds AI prompt-template docs for migration, modernization, and new-test authoring, and wires them into site navigation and doc publishing

Issue references

Closes #129
Closes #130
Closes #131

Additional included docs work

This PR also includes AI-assisted workflow documentation:

• reusable prompt templates for migration, modernization, and new test authoring
• navigation updates so those docs appear in the published doc set
• replacement of the older migration-only Copilot prompt page with the broader AI prompt-template page

No dedicated issue was found for that AI-doc expansion, so it is included here as related documentation work in the same PR.

[Copilot]

Pull request overview

Documentation-focused PR that refreshes FastMoq’s public-facing docs for v4 evaluation, aligns roadmap wording with the public backlog (including a new detailed generator planning page), and adds AI prompt-template documentation with navigation/publishing updates.

Changes:

• Updated top-level and docs-site navigation to surface Feature Parity and new AI prompt templates; removed the older migration-only Copilot prompt page.
• Reworked roadmap docs to separate concise roadmap notes from detailed v5 generator planning/design.
• Refined framework-neutral wording across docs and expanded the feature-parity page into a clearer comparison aid.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
toc.yml	Adds nav entries for Feature Parity, AI prompt templates, and generator roadmap; removes old Copilot prompts entry.
docs/roadmap/generator-roadmap.md	New detailed v5 generator roadmap/design companion page.
docs/roadmap/README.md	Updates roadmap framing, aligns with public backlog, and links to generator roadmap.
docs/migration/provider-and-compatibility.md	Refocuses provider-default guidance and routes detailed mechanics to provider-selection docs.
docs/migration/copilot-prompts.md	Removes the older migration-only Copilot prompt templates page.
docs/migration/README.md	Repoints AI-assistance entry links to the new AI prompt templates page.
docs/getting-started/testing-guide.md	Adds a pointer to AI prompt templates.
docs/getting-started/provider-selection.md	Clarifies framework-specific startup hook examples as parallel options (not product modes).
docs/getting-started/README.md	Adds AI prompt templates pointer and clarifies xUnit usage as example-only.
docs/feature-parity/README.md	Expands parity/comparison content and adds more detailed examples and guidance.
docs/cookbook/README.md	Clarifies xUnit usage as example-only.
docs/ai/README.md	New AI prompt templates page for migration, new tests, and modernization workflows.
docs/README.md	Wires AI workflows into the docs home and updates section descriptions (feature parity/roadmap).
docfx.json	Includes docs/ai/**.md in DocFX content for publishing.
README.md	Refreshes the repo landing page to be evaluation-oriented and test-framework agnostic, with updated doc links.