Print hint when config load exceeds 500ms #1231

Summary

When vp spends more than ~500ms loading the local config we should close the run with a gentle hint so folks know where to look for tuning guidance.

Motivation

Slow config discovery/merging usually means project-specific overrides or expensive plugin setup. Surfacing a pointer to the config docs right after the command finishes gives people a next step instead of silently eating the latency.

Proposal

• Measure config load duration for every vp command that loads the project config.
• If it exceeds 500ms, append a one-line hint at the very end of the command output (after existing summaries) such as:

  hint: config took 640ms to load – see https://viteplus.dev/config/ for cleanup tips
  

• Ensure:
  • Only prints once per run
  • Respects --json / --silent modes (do not emit in structured output scenarios)
  • Uses the actual measured duration in the message

Acceptance Criteria

• Commands that trigger slow config loads (>500ms) show the hint exactly once at the end.
• Fast runs (<500ms) show no extra output.
• Link points to https://viteplus.dev/config/.
• Covered by a test (unit or integration) that exercises both the <500ms and >500ms paths.