Batched a few minor edits to Profiles Sync, Spec Semantic, and Test Connections

Documentation consistency and clarity:

• Standardized document titles to use sentence case for consistency (src/connections/test-connections.md, src/unify/profiles-sync/overview.md). [1] [2]
• Reworded descriptions of Segment's testing tools for improved clarity and conciseness (src/connections/test-connections.md).
• Improved phrasing regarding standardized event names and properties in the semantic events spec documentation (src/connections/spec/semantic.md).
• Clarified the list of event types in the Event Tester instructions by adding "and" for completeness (src/connections/test-connections.md).

Support and tone improvements:

• Updated support contact language to use a more direct and customer-friendly tone ("contact Segment support" and "we'll help you") (src/connections/test-connections.md).

Proposed changes

Merge timing

Related issues (optional)

[DOC-1260][DOC-1261]