feat: add member relationship model and improved interaction graph UX

[n-WN]

Summary

• add a new member relationship model that fuses @ mentions, temporal adjacency, and reciprocity
• expose relationship graph APIs through worker, IPC, preload, and shared types
• redesign interaction visualization with better force-layout tuning, edge readability, focus mode, and side insight panel
• add model controls (weights/window/decay/thresholds), core/full relation view, and relation filtering controls
• add a CLI script and docs for generating relationship graph artifacts from sample data
• fix migration/session scanning by skipping non-chat databases (prevents false migration prompts)

Verification

• pnpm run build passes locally
• relationship analysis script runs on the provided sample dataset

Notes

• local temporary artifacts in .tmp/ and sample outputs in data/ are intentionally not included in this PR

[n-WN]

This PR is superseded by #77, which contains the same changes split into focused commits for easier review.

[n-WN]

Closing in favor of #77 (split commit history).