refactor(scenario): only 2 scenarios (social / face-to-face); 're-contact' becomes a persona trait

- Scenario picker now has only social + f2f_call (removed recontact) in backend
  _scenarios, start_session validation, and Chat.vue picker.
- 'ลูกค้ากลับมาติดต่อ' is no longer a scenario: it's now a PERSONA trait. Persona prompt
  generates ~1-in-4 personas with recontact=true (asked before, now returns warmer/ready);
  store shape gets recontact field; simulator injects a re-contact note into the persona's
  system prompt so it plays as a returning customer naturally.
- test_scenario updated: unknown scenario defaults to social; recontact shown as a
  generated persona trait.
All 9 backend suites pass. Rebuilt dist.

frontend/dist/assets/Personas-cgqlaBh7.css

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+.grid[data-v-ec851b01]{display:grid;grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:14px}.pcard[data-v-ec851b01]{display:flex;flex-direction:column;min-height:190px}.diff[data-v-ec851b01]{margin:8px 0}.star[data-v-ec851b01]{color:#d8dbe3}.star.on[data-v-ec851b01]{color:#f59e0b}.badge.won[data-v-ec851b01]{background:#dcfce7;color:#166534}.badge.lost[data-v-ec851b01]{background:#fee2e2;color:#991b1b}.badge.not_tried[data-v-ec851b01]{background:#eef2ff;color:#4338ca}.guide[data-v-ec851b01]{background:#eef2ff;border-color:#c7d2fe;margin:12px 0 16px}