chore: clean hydrotech-beam syncthing conflicts and add new docs

- Remove all .sync-conflict-* files
- Remove temp _temp_part_properties.json files
- Add USER_GUIDE.md
- Add dashboard docs (Executive, Technical, Operations, Master Plan)
- Add playbooks (DOE, NX_REAL_RUN, SYNCTHING_RECOVERY)
- Update iteration results

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

projects/hydrotech-beam/studies/01_doe_landscape/iterations/iter006/results.json

@@ -1,6 +1,6 @@
 {
   "iteration": 6,
-  "mass_kg": NaN,
+  "mass_kg": 1085.4467002717115,
   "tip_displacement_mm": 17.468721389770508,
   "max_von_mises_mpa": 108.2625078125,
   "feasible": false,