style(app): apply rustfmt to satisfy CI format check (#1954)

[Seha16]

Summary

• The linux branch fails cargo fmt --all -- --check under the pinned 1.93 toolchain (rustfmt 1.8.0), turning the Fast checks CI job red before build / clippy / tests run.
• This runs cargo fmt --all over the two drifted files (crates/app/src/ui/app/mod.rs, crates/app/src/ui/browse_tab.rs): a stray blank line and a few builder chains collapsed to fit max_width = 120.
• Formatting only, no behavior change (2 files, +4 / -12). Fixes Linux: cargo fmt --all -- --check fails on linux branch (Fast checks CI red) #1954.

Test plan

• cargo fmt --all -- --check (clean)
• cargo clippy --all-targets -- -D warnings (clean)
• cargo build --workspace (exit 0)
• cargo test --workspace --lib (148 passed, 1 ignored)

No UI/visual change (formatting only), so no before/after screenshots apply.

[datlechin]

Thank you