docs(community): add Specstride to Community Friends

[mairp]

Description

Adds Specstride to Community Friends (docs/community/friends.md), at the bottom of the list.

Specstride builds on Spec Kit. It takes a feature's tasks.md as its input and drives a coding agent through the phases one at a time. spec.md, plan.md and contracts go along as read-only context. A separate LLM critic has to approve each phase's evidence before the next phase starts. Its --reverse mode can also produce a Spec Kit layout from an existing codebase. The project is Apache-2.0 and maintained; v0.1.0 was released today.

It is independent and not affiliated with GitHub. The entry follows the page's existing note.

Testing

• Docs-only change: one list entry, same format as its neighbours; checked the link resolves.
• Tested locally with uv run specify --help (n/a, no code change)
• Ran existing tests (n/a, no code change)

AI Disclosure

• I did not use AI assistance for this contribution
• I did use AI assistance (fill in the disclosure below)

AI disclosure: Claude Code (Claude Opus 5.5), human-supervised. It drafted the one-paragraph entry and opened this PR at my request. I reviewed the text, and it describes my own project accurately. Docs only, no code.