docs(#3997): add missing sidebar entries for behaviour docs

[fullsend-ai-coder]

Add sidebar entries for behaviour-testing and behaviour-drivers to the Development section of the VitePress config. These docs exist in docs/guides/dev/ and are linked from the guides README but were missing from the sidebar navigation.

---

Closes #3997

Post-script verification

• Branch is not main/master (agent/3997-add-sidebar-entries)
• Secret scan passed (gitleaks — 1e0b37eebf2aff1964d5751826d60db9cfbd5341..HEAD)
• Pre-commit hooks passed (authoritative run on runner)
• Tests ran inside sandbox

[github-actions]

Site preview

Preview: https://9fb7f33f-site.fullsend-ai.workers.dev

Commit: 33d6ace7e4eb9ccb7f91c6704747f5913685e5c3

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[fullsend-ai-retro]

🤖 Finished Retro · ✅ Success · Started 11:05 AM UTC · Completed 11:12 AM UTC
Commit: 33d6ace · View workflow run →

[fullsend-ai-retro]

PR #4008 was a clean, zero-rework execution of the retro→triage→code→merge pipeline. The retro agent identified 2 remaining missing VitePress sidebar entries (issue #3997) while reviewing PR #3868, which itself fixed 3 sidebar issues from PR #3398. The triage agent classified it correctly in ~3 minutes, the code agent produced a correct 2-line fix in ~7 minutes, and a human reviewer approved and merged within 34 minutes total. The review agent did not dispatch — this is a known gap already tracked in issues #3996 and #3998. The main improvement opportunity is systemic: sidebar drift between docs/ directories and the VitePress config.ts sidebar has now required 3 separate fix PRs. A CI lint check would catch this class of drift at PR time.

Proposals filed

• Add CI lint check to verify VitePress sidebar coverage for manually-managed sections (in fullsend-ai/fullsend)