[vinayagg]

Summary

• Replace the manual folder path and setup controls with one Select folder action per input/output location.
• Recognize existing identity markers, create a marker only for an unmarked folder selected on the owning client, and reject mismatched folders without changing mappings or markers.
• Move synchronization checks into a collapsed section and update the documentation and tests.

Validation

• node --test dsh-runtime/plugin/lib/thread-shared-folders.test.js dsh-runtime/plugin/lib/thread-folder-settings.test.js — 11 passed.
• npm run check — typecheck passed; the client suite had three failures outside this change: thread-review.test.js and thread-runner.test.js import thread-applications.js, which is absent on main, and thread-credits.test.js expects https://bees.bot but receives https://old.example.
• PR CI: the Linux build job reproduces the two missing-import failures (its credits test is skipped). The secret-scan job failed twice before scanning because GitHub returned HTTP 504 for the pinned gitleaks release download.