Feature: carry community labels over re-clustering via member-overlap matching (invalidation exists, carry-over does not) #1653

Version: graphifyy 0.9.5.

Problem

Community labels are keyed by community ID, which drifts on every re-clustering. 0.9.5 correctly invalidates stale labels (per-community signatures) but cannot carry them over: every cluster-only forces a manual re-labeling of the top-N. We've done this 4 times — 30 to 46 communities re-labeled by hand each time, for communities whose membership barely changed.

Proposal

Match old↔new communities by member overlap (Jaccard above a threshold) and carry the existing label over; only genuinely new/changed communities need fresh labels.

Bonus: a claude-subagents labeling backend (like extraction already has) for users without a Gemini key.

Related: #1027 (closed — fixed misalignment/invalidation, but carry-over is the missing half).