[Draft] Add Accessibility Apis

[sakhisheikh]

AX: Directional navigation + label-based WDA action

• Add Direction navigation (Next/Previous); refactor move to accept direction.
• Track currentFocusedLabel and labelTraverseCount; Next++ and Previous-- (min 1).
• WDA action: find by label, select by visit index, tap center via testobject/tap.
• Add audit runner endpoint and background drains for audit issue/log streams.
• Endpoints:
  • POST /device/:udid/accessibility/{next,previous}
  • POST /device/:udid/accessibility/perform-action
  • POST /device/:udid/accessibility/wda/perform-action
  • POST /device/:udid/accessibility/audit/run