Group recall by bags with a per-project recall mode #296

See #290, section 3 (recall). Depends on the bags subtask.

Work

• Grouped recall lists top-level memories only. A bag line shows its summary, the number of visible children and their titles, shortened to fit the budget: [#48] Deployment: … • 7 submemories: A, B, C, ….
• Default mode auto: flat below the top-level threshold, grouped above it. Project setting (settings tab and project_update) for auto, flat or grouped and the threshold.
• Critical memories keep their reserved budget in both modes.

Acceptance

• Recall output tests for flat, grouped and auto at the threshold boundary.
• Child titles in a bag line respect visibility.
• Recall stays within maxChars in every mode.