[codex] remove unused src-tauri mirror rust modules

[mxyhi]

Summary

This PR removes a set of unused Rust mirror modules under src-tauri/src/antigravity, src-tauri/src/kiro, and src-tauri/src/codex.

These files were historical copies of implementations that now live in crates/token_proxy_core. The active mod.rs files in those three src-tauri module directories already re-export the core implementations directly, so the local mirror files were not part of the effective module graph.

User-facing impact

There is no intended user-visible behavior change.

The effect of this cleanup is reducing dead code in the Tauri layer, lowering maintenance cost, and removing a misleading source of truth that could cause future edits to land in files that are never compiled or executed.

Root cause

src-tauri/src/antigravity/mod.rs, src-tauri/src/kiro/mod.rs, and src-tauri/src/codex/mod.rs each re-export token_proxy_core with pub use token_proxy_core::<module>::*;.

That means the sibling Rust files in those directories were bypassed by the current module boundary. They remained in the repository as mirror copies, but they were not the code path used by the application.

Fix

The PR deletes the unwired mirror files and keeps the mod.rs re-export entrypoints intact.

The cleanup covers:

• src-tauri/src/antigravity/*.rs except mod.rs
• src-tauri/src/kiro/*.rs except mod.rs
• src-tauri/src/codex/*.rs except mod.rs

No frontend files or JS dependencies are changed in this PR.

Validation

I verified the cleanup with:

• cargo check --workspace --all-targets
• cargo test --workspace --all-targets

Results:

• src-tauri tests: 4 passed
• token_proxy_core tests: 216 passed
• No frontend or dependency diff remains in package.json, pnpm-lock.yaml, or src/