Clean up train rendering traits

[scaryrawr]

The train renderer supported both real terminals and the web terminal through a combined display trait, but that made the boundary feel awkward: geometry, drawing, and failure handling were all tied together. This PR separates those concerns so the core renderer has a more natural API for both adapters.

Summary

• Replaces the old Rust-facing Display/Options traits with explicit ScreenSize, TrainOptions, RenderTarget, and RenderError types.
• Updates libsl rendering helpers and train entrypoints to pass dimensions separately and propagate render-target failures instead of requiring adapter-level unwraps.
• Adapts the CLI and WASM wrappers to the new core API while preserving terminal behavior and the JS-facing WASM shape.
• Adds focused libsl tests for clipping, offscreen completion, and target error propagation.

Validation

• cargo fmt --all
• cargo test --workspace
• bun run test:websl
• bun run build:websl
• bun run typecheck:page
• bun run test:page
• cargo run -p sl -- --help

[Copilot]

Pull request overview

This PR refactors libsl’s rendering interface to separate screen geometry, render options, and drawing/error handling so both the CLI terminal adapter and the WASM adapter can use a more natural core API.

Changes:

• Replaces the old Display/Options traits with ScreenSize, TrainOptions, RenderTarget, and RenderError, and updates train entrypoints accordingly.
• Updates core rendering helpers (mvaddstr, add_train, smoke/man helpers) to take explicit screen dimensions and propagate target draw failures.
• Adapts the CLI and WASM bindings to the new API and adds focused libsl tests for clipping/offscreen/error propagation.

Show a summary per file

File	Description
libraries/websl/src/lib.rs	Updates WASM bindings to the new RenderTarget + ScreenSize/TrainOptions API and maps core errors into JS-visible outcomes.
libraries/libsl/src/mvaddstr.rs	Refactors clipping/drawing helper to take ScreenSize + RenderTarget and return target errors; adds unit tests.
libraries/libsl/src/logo.rs	Updates logo train entrypoint signature to the new rendering API types.
libraries/libsl/src/lib.rs	Introduces ScreenSize, TrainOptions, RenderTarget, and RenderError as the new public core rendering surface.
libraries/libsl/src/d51.rs	Updates D51 entrypoint to new API and adds an offscreen regression test.
libraries/libsl/src/c51.rs	Updates C51 entrypoint to new API.
libraries/libsl/src/add_train.rs	Refactors the main renderer loop to accept screen/options separately and propagate RenderTarget failures.
libraries/libsl/src/add_smoke.rs	Updates smoke helper to use RenderTarget and return errors instead of swallowing failures.
libraries/libsl/src/add_man.rs	Updates “man” helper to use RenderTarget and return errors instead of swallowing failures.
apps/sl/src/main.rs	Adapts the CLI renderer to RenderTarget and properly distinguishes offscreen completion vs target I/O errors.

Copilot's findings

• Files reviewed: 10/10 changed files
• Comments generated: 3