refactor: resolve move_items.rs + move_items/ directory duality

[chubes4]

Problem

There is both a file and a directory with the same stem name:

src/core/refactor/move_items.rs       (700 lines — main move logic)
src/core/refactor/move_items/         (5 files — supporting types)
    ├── extension_integration.rs
    ├── item_kind.rs
    ├── move_options.rs
    ├── types.rs
    └── whole_file_move.rs

This is a Rust module anti-pattern. Having both move_items.rs and move_items/ at the same level creates confusion about which is the "real" module root. Rust 2021 edition supports this layout, but it's widely considered a code smell.

Proposed Fix

Rename move_items.rs → move_items/mod.rs, making the directory the single source of truth:

src/core/refactor/move_items/
├── mod.rs                      (current move_items.rs content)
├── extension_integration.rs
├── item_kind.rs
├── move_options.rs
├── types.rs
└── whole_file_move.rs

Constraints

• No behavioral changes
• All imports and re-exports preserved
• cargo test and cargo clippy clean

Related

• audit: god file in homeboy (20) #536 (god file audit finding — move_items.rs is 700 lines, so under threshold, but addressing the structural issue)