docs: wrap up the playtest-1 redesign round

[jdpigeon]

Docs only.

• TODOS:
  • resolves the playtest-1 P0s that WS6/WS7 fixed;
  • flags the Collect pre-run screen as never redesigned;
  • adds the WS8 manual QA pass and second-playtest items;
  • records the findings from this round: Lato is not bundled, Run & record with an ended-early session, fixture marker doubling, the Explore stall watchdog, the tips layout, and CI has no flow tests;
  • drops the Phase 2 reviewer polish item that WS6: integrate the approved Clean design #285 resolved;
  • adds the round to Done recently.
• ROADMAP: V1.5 is now the playtest-driven redesign, with WS1–WS7 checked off and WS8 plus a fixes PR still to do.
• docs/user-flow.md: new diagram and Home, Prepare, Collect and Explore sections for the redesigned app.
• Removed the implemented WS2/WS5/WS5b plans; git history keeps them.