A release build can take its app folder from the working directory #956

Problem

At start the desktop shell looked for its app root in the current working directory before looking beside its own executable. That probe exists for development runs. In a release build, an exe started from a terminal whose current folder is a StemDeck source checkout used that checkout as its app root instead of its own folder, so it ran the wrong backend against the wrong data.

Who is affected: anyone who starts a release or portable build from a terminal inside a StemDeck project folder. Rare, but silent.

Where

• desktop/src-tauri/src/main.rs:5398 app_root
• desktop/src-tauri/src/main.rs:5430 cwd_repo_root

Current state

Fixed in PR #891 (merged into big-release, ships with 0.21.0).

Proposed fix

What the merged fix does: the working directory probe lives in cwd_repo_root(cwd, debug_build), and app_root passes cfg!(debug_assertions). A release build skips it and goes from STEMDECK_ROOT straight to the folder beside the executable. Debug runs keep the probe.

Verification

• cargo test --manifest-path desktop/src-tauri/Cargo.toml only_debug_builds_take_the_app_root_from_the_working_directory
• By hand: open a terminal in a StemDeck checkout, start a release StemDeck.exe that lives in another folder by its full path, and confirm it runs the backend beside that exe, not the one in the checkout.