Restrict the view to a selected region or subset of objects #72

Problem

Auto-seg ROIs (~5×5 µm) are too dense; users proofread a small area but still have to load/see everything, which slows every operation.

Proposed

Let the user constrain the working view to a subset — by selecting objects (show only these) or drawing a region (hide everything outside) — while keeping the rest available to bring back.

Notes

Weiling's request. Related to Issue A but distinct (spatial/subset scoping vs. flipping a selection). Vijay noted a smaller ROI could also be cut at .jser-creation time; in-app scoping avoids juggling multiple chasers. Acceptance criteria to be firmed up with users.