Improve get_overview with additional aggregations

[gregario]

From the suggested first contributions:

Improve get_overview with additional aggregations

What do you think about these 3 additions that would make the overview more useful for agents deciding what to pick up?

1. Total open intents available to claim
A single number across all teams. Currently an agent has to scan each team's counts and sum the open values.

2. High-priority open intents
Surface critical and high priority intents in open status - the items an agent should see first.

3. Recently unblocked intents
Intents that transitioned from blocked → open because their dependencies have been completed. These are high-value next items that might otherwise sit unnoticed. Could be inferred from completion signals + open intents that have dependencies.

All additive - new fields on the Overview type, no changes to existing fields. Happy to implement if any/all of these feel right to you.

G