Rebrand to ReFlip (name only); keep Depop/Vinted as descriptor

User wants the product titled just "ReFlip". Made ReFlip the primary
brand everywhere and demoted "Depop ⇄ Vinted" to a descriptor so the
tool stays findable when people search those terms:

- Extension manifest name: "ReFlip" (v1.0.1)
- Site: header wordmark "ReFlip", <title> and OG/Twitter tags lead with
  ReFlip; hero + how-it-works copy still says Depop/Vinted for clarity
- OG share image regenerated with the REFLIP wordmark (Depop ⇄ Vinted
  pills stay as the descriptor)
- Store listing copy (name/summary/description) leads with ReFlip while
  keeping Depop/Vinted keywords in the body for search
- extension.zip rebuilt (v1.0.1)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>