[Wei Weng (weng271190436)]

What this PR does / why we need it

/kind documentation

• Replace the directory inventory and stale tooling advice with a concise, Makefile-backed command matrix.
• Document hub/member and Traffic Manager boundaries.
• Explain envtest prerequisites and targeted validation, separate local tests from Azure E2E, and require explicit approval for live Azure operations.
• Remove references to absent domain-knowledge/specification paths.
• Require planning approval and breadcrumbs only for non-trivial work, without repeated approval for an already-approved plan.

Validation

• Passed local documentation contract checks: 22 relative links/anchors, Make-command references, Markdown structure, targeted test-package example, and requested guidance.
• Passed git diff --check; Go style guide URL returned HTTP 200.
• Go builds, make reviewable, and runtime/E2E tests were not run: this changes Markdown only.

Reviewer notes

Standalone PR based on current main, not the Gateway feature branch. No runtime, workflow, dependency, or unrelated worktree changes.