Improve geometry-aware tag readability

[epowell40]

What changed

• model tag leaders as bounded view-plane segments and reject leader crossings
• protect annotation, room-tag, target, and new-work content
• prefer nearby clear plan space over walls, equipment, and routed MEP elements
• validate measured tag bounds and actual Revit leader geometry before retaining created work
• fail closed on unmeasurable leaders and unsupported geometry-aware spatial tag kinds
• retry bounded leader-collision failures in the deterministic level-tag runtime

Why

Engineering drawings need readable tags: short leaders, no crossing leaders, clear tag heads, and explicit safe failure in dense views.

Validation

• public common tests: 192/192
• public backend tests: 942 passed, 3 skipped, 0 failed
• focused planner/policy tests: 27/27
• deterministic level-tag runtime: 6/6
• tool contracts: 195/195
• skill manifest: 21/21
• Revit add-in solution: 0 errors; 4 established assembly-version warnings
• independent Terra High read-only review completed