feat(components): intrinsic measurement for terminal, table and codeblock

[LeadcodeDev]

Goal: Terminal, Table and Codeblock measure their own content so they size correctly inside flex containers without explicit width/height.

Evidence: box_builder.rs:222-232 registers intrinsics only for Text, GradientText, Caption, Kbd, Counter, Badge.

Invariants: explicit size still wins; auto_scroll semantics unchanged.

Acceptance: a terminal without explicit size inside a flex column gets a non-zero measured height; layout tests cover the three components.

Files: crates/rustmotion-components/src/intrinsic.rs, box_builder.rs, the three painters.

Verify: cargo test --workspace