crate consolidation: delete orphaned tui-core crate

[Hmbown]

Problem

crates/tui-core is a 192-line crate containing a UiState / UiEvent / UiEffect enum scaffold. Nothing in the workspace depends on it — zero use codewhale_tui_core references anywhere in the tree. It appears to be an early scaffolding artifact that was never wired into the real TUI (crates/tui, 230K lines).

Plan

1. Remove "crates/tui-core" from [workspace.members] in root Cargo.toml
2. Delete crates/tui-core/ directory

Verification

• cargo check --workspace passes
• cargo build --workspace passes
• No remaining references to tui-core or codewhale_tui_core in the tree

Impact

Zero functional change. Purely removing dead code.