Title: Colorize get pr insight and group sections by risk

[BlueLabelscotch]

Description:

• "Code Overview" box: renamed from "Insight", rendered in Unicode box borders, heading colorized red/yellow/green by risk.
• get pr:review_group: replaced numbered "Group 1/2" headers with a risk-colored "●" bullet + plain title + colorized [risk] tag.
• Diff-stat (+N/-M) annotations were considered but dropped — the /pullreq/{id}/view endpoint doesn't return addition/deletion counts per file, we have to make like N+1 api calls for the data, so it's deferred pending a cheaper data source.