feat: member relationship model with split commits

[n-WN]

Supersedes #76 with a cleaner commit history split by concern.

Commit breakdown

1. feat(interaction): implement relationship graph model and IPC APIs
2. fix(database): skip non-chat sqlite files in migration and session scan
3. feat(ui): redesign relationship graph with focus and insight panel
4. docs(tooling): add relationship model CLI generator and guide

Verification

• pnpm run build passes locally
• relationship analysis script runs on sample data

Notes

• .tmp/, data/, and local pnpm-lock.yaml changes are intentionally excluded