Align doctor with reportable session sources

[luoyuctl]

Summary

• make doctor use reportable session discovery so SQLite-backed legacy file dirs are skipped like TUI/overview
• include SQLite-backed Hermes/OpenCode DB sources in doctor output
• add a doctor regression test covering Hermes DB + skipped legacy files

Real local verification

• agenttrace --doctor now reports Sessions: 1714
• Hermes legacy file source shows 0 while Hermes Agent (DB) shows 510
• OpenCode storage source shows 0 while OpenCode (DB) shows 188
• agenttrace --overview -f json also reports 1714 total sessions

Tests

• go test ./cmd/agenttrace ./internal/engine ./internal/tui
• go build -o /tmp/agenttrace-doctor-fix ./cmd/agenttrace
• go test ./...