mecatui: migrate soul inspector to bounded.Viewport #1899

Scope

Migrate the read-only soul/persona inspector in cmd/mecatui/ui/soul.go to bounded.Viewport if its existing behavior is retained.

Current behavior

It owns an explicit scroll offset over wrapped content with a fixed 12-row card. Keyboard supports line/page/home/end; wheel is consumed but does not move content.

Required outcome

• Centralize physical-line offset and geometry without changing the deterministic fixed-height card policy.
• Preserve existing keyboard behavior and the current wheel-consumption policy unless a separately approved behavior change says otherwise.
• Keep card chrome and overflow wording local.

Verification

Add scenario-first acceptance coverage and run focused soul/UI and bounded tests before project gates.