Chore/check root markdown formatting

[dhruv8sh]

Summary

• Extend the format-docs CI job to check root-level Markdown (AGENTS.md, README.md, FAQ_POC.md, etc.) with Prettier, closing the gap where only docs/ was covered
• Normalize existing formatting drift in the three root files that were failing (AGENTS.md, FAQ_POC.md, ProjectGovernance.md) — whitespace/list-marker only, no content changes
• Document the new gate in AGENTS.md's CI Gates checklist

Changes

File	Change
.github/workflows/format.yml	Added a step to the format-docs job that runs docs/node_modules/.bin/prettier --config docs/.prettierrc --check "*.md" from the repo root, reusing the already-installed binary and the existing docs/.prettierrc config
AGENTS.md	Reformatted (Prettier drift only); added item 8 to the CI Gates list documenting the new root-Markdown check
FAQ_POC.md	Reformatted (Prettier drift only)
ProjectGovernance.md	Reformatted (Prettier drift only)

Closes #1093

Test plan

• Docs format: cd docs && npm run format
• Root Markdown format: docs/node_modules/.bin/prettier --config docs/.prettierrc --check "*.md" (run from repo root)
• Ran the format-docs and check-claude-md-symlink GitHub Actions jobs locally via act — both pass, including the new step
• Verified CLAUDE.md still resolves as a symlink to AGENTS.md (git ls-tree mode 120000) after formatting AGENTS.md
• cargo test-fastly && cargo test-axum
• cargo clippy-fastly && cargo clippy-axum
• cargo fmt --all -- --check
• JS tests: cd crates/trusted-server-js/lib && npx vitest run
• JS format: cd crates/trusted-server-js/lib && npm run format
• WASM build: cargo build --package trusted-server-adapter-fastly --release --target wasm32-wasip1
• Manual testing via fastly compute serve
• Other: docs-only change, no Rust/JS code touched — Rust/JS gates are unaffected and not re-run

Checklist

• Changes follow AGENTS.md conventions
• No unwrap() in production code — use expect("should ...")
• Uses tracing macros (not println!)
• New code has tests — N/A, CI workflow change and Markdown-only edits
• No secrets or credentials committed