feat(reflect): add broader reflection signals

[zhexulong]

What's changed?

• Add deterministic source-role, project-activity, and task-shape summaries to recall-reflect reports.
• Render broader signal sections after the timeline in text output while keeping JSON changes additive.
• Cover the new report fields with unit tests and CLI JSON coverage that preserves the metadata/messages export contract.
• Update the Reflect KEP to mark broader signals as the completed milestone and keep interactive review as the next step.

Why

• Broaden personal and project reflection without moving workflow logic into Recall core or reading SQLite directly.

Verification

• cargo test -p recall-reflect reflect_report_summarizes_project_activity
• cargo test -p recall-reflect reflect_cli_json_exposes_broader_signals
• make check
• cargo test integration::eval_harness
• Oracle review found one determinism issue; fixed with BTreeSet source ordering and regression coverage.