[ChangAn-1314]

Summary

• raise the Axum request body limit from the default 2 MiB to a bounded, configurable limit
• resolve bin/pi-switch.js from the package root when the native TUI starts a daemon outside the repository directory
• add a regression test covering model requests larger than Axum's default limit

Problem

Large multimodal requests can exceed Axum's default 2 MiB body limit and fail before reaching the proxy handler with:

413 Failed to buffer the request body: length limit exceeded

Separately, the native TUI starts daemons without a project_dir argument. When pi-switch tui is launched outside the repository, daemon startup falls back to the current working directory and fails with:

pi-switch.js not found at "bin/pi-switch.js"

Changes

• apply DefaultBodyLimit to the proxy router
• default to 32 MiB and allow PI_SWITCH_MAX_REQUEST_BODY_MIB values clamped to 4-256 MiB
• export PI_SWITCH_PROJECT_DIR from the JavaScript entrypoint
• consult that package root before executable-relative and current-directory fallbacks in the native daemon path resolver
• enable Tower's util feature for router regression testing
• format only the Rust modules changed by these fixes, as required by the repository CI

Verification

• cargo test: 16 passed
• pnpm build:native
• node --check bin/pi-switch.js
• changed-file rustfmt --check
• CI Rust/WebUI verification
• CI native builds for Linux GNU, Linux musl, Windows x64, macOS x64, and macOS ARM64