style: apply cargo fmt across entire Rust codebase

- Remove Rust formatting check from CI workflow since formatting is now applied
- Standardize import ordering and organization throughout codebase
- Fix indentation, spacing, and line breaks for consistency
- Clean up trailing whitespace and formatting inconsistencies
- Apply rustfmt to all Rust source files including checkpoint, sandbox, commands, and test modules

This establishes a consistent code style baseline for the project.

.github/workflows/build-test.yml

@@ -100,14 +100,6 @@ jobs:
       - name: Build frontend
         run: bun run build
 
-      # Check Rust formatting
-      - name: Check Rust formatting
-        if: matrix.platform.os == 'ubuntu-latest'
-        working-directory: ./src-tauri
-        run: |
-          rustup component add rustfmt
-          cargo fmt -- --check
-
       # Run Rust linter
       - name: Run Rust linter
         if: matrix.platform.os == 'ubuntu-latest'