Remove collision-era language from docs and code

- Updated FAQ.md, ADVANCED.md, TROUBLESHOOTING.md to explain hash IDs eliminate collisions
- Removed --resolve-collisions references from all documentation and examples
- Renamed handleCollisions() to detectUpdates() to reflect update semantics
- Updated test names: TestAutoImportWithCollision → TestAutoImportWithUpdate
- Clarified: with hash IDs, same-ID = update operation, not collision

Closes: bd-50a7, bd-b84f, bd-bda8, bd-650c, bd-3ef2, bd-c083, bd-85a6

FAQ.md

@@ -286,12 +286,11 @@ When two developers create new issues:
 
 Git may show a conflict, but resolution is simple: **keep both lines** (both changes are compatible).
 
-For ID collisions (same ID, different content):
-```bash
-bd import -i .beads/issues.jsonl --resolve-collisions
-```
+**With hash-based IDs (v0.20.1+), same-ID scenarios are updates, not collisions:**
 
-See [ADVANCED.md#handling-import-collisions](ADVANCED.md#handling-import-collisions) for details.
+If you import an issue with the same ID but different fields, bd treats it as an update to the existing issue. This is normal behavior - hash IDs remain stable, so same ID = same issue being updated.
+
+For git conflicts where the same issue was modified on both branches, manually resolve the JSONL conflict (usually keeping the newer `updated_at` timestamp), then `bd import` will apply the update.
 
 ## Migration Questions