fix(dev): isolate Cargo targets per worktree

[johnmatthewtennant]

Summary

Berd currently directs interactive Cargo commands from every checkout on a machine to one target directory. Concurrent just dev, test, check, and Clippy processes then serialize on the Cargo artifact lock.

Default development Cargo output to each checkout's ignored src-tauri/target directory on Unix and Windows, while preserving BERD_TAURI_CARGO_TARGET_DIR as an explicit override. Unix just bundle and just bundle-debug retain the shared bundle target expected by existing packaging consumers.

Reviewer-reproducible examples

Resolve development and bundle targets separately:

bash scripts/resolve-tauri-cargo-target-dir.sh
bash scripts/resolve-tauri-cargo-target-dir.sh bundle

The first prints the checkout's src-tauri/target. On macOS, the second prints ~/Library/Caches/berd-tauri/cargo-target.

An explicit override remains unchanged in either scope:

BERD_TAURI_CARGO_TARGET_DIR=/tmp/berd-target bash scripts/resolve-tauri-cargo-target-dir.sh
BERD_TAURI_CARGO_TARGET_DIR=/tmp/berd-target bash scripts/resolve-tauri-cargo-target-dir.sh bundle

[morgmart]

🤖 Automated code review

APPROVE. Corrected the completed Engineering review artifact after re-checking the exact three-dot comparison 20c005a...0574251 and the supplied current changed-line anchors. The five changed files consistently isolate development Cargo targets by checkout while retaining the explicit override and shared Unix bundle target contract. No publishable or duplicate-suppressed finding remains. The supplied GitHub evidence was inspected and is structurally valid for the exact base and head; all ten supplied check runs succeeded, while required checks independently govern merge readiness.

Deterministic publication result: 0 blocking and 0 non-blocking inline finding(s) publishable; 0 duplicate(s) suppressed; 0 blocking screenshot-evidence requirement(s) in this review body.

Pending checks: 1 check(s) are not complete.

This approval reflects the completed code review only; merge readiness remains governed by the repository's required checks.