Fix formatting in README workflow diagram

[kigiri]

This was bothering me

  DEFINE         PLAN          BUILD        VERIFY        REVIEW         SHIP
 ┌──────┐      ┌──────┐      ┌──────┐      ┌──────┐      ┌──────┐      ┌──────┐
 │ Idea │ ──▶ │ Spec │ ──▶ │ Code │ ──▶ │ Test │ ──▶ │  QA  │ ──▶ │  Go  │
 │Refine│      │  PRD │      │ Impl │      │Debug │      │ Gate │      │ Live │
 └──────┘      └──────┘      └──────┘      └──────┘      └──────┘      └──────┘
  /spec         /plan         /build        /test         /review       /ship

[zohaib545]

Looking great! Thanks

[Taengsil]

Unless diff shows incorrectly, the boxes are still misaligned.

[federicobartoli]

Conservative and sensible fix — keeps Unicode arrows (which render fine on GitHub), trims one ─ per arrow, and tightens label spacing. Good improvement over the original alignment without the regression of the parallel #140 (which converts to ASCII --->).

Small nit: a before/after screenshot in the PR description would have helped reviewers see the alignment change at a glance, but the result speaks for itself in a fixed-width view.