Build labelled benchmark set for production validation

[sonianayak66]

Create a larger labelled benchmark set using clean CAD exports, scanned drawings, screenshots, and phone/monitor captures.

Acceptance criteria:

• Include labelled bubble boxes/circles, bubble numbers, leader-line endpoints, and target dimension text.
• Track accuracy by image type and quality level.
• Store benchmark manifest and scoring notes without hard-coded expected values inside detection logic.
• Add regression thresholds for bubble recall, assignment accuracy, and low-confidence review rate.