refactor: Migrate engine native command planning (#13533)
## Intent
Continue Phase 4: engine/run execution should plan native commands from
the **native-task catalog + TaskArgs**, producing an ecosystem-neutral
`TaskCommand` without calling `Toolchain::task_command`.
**Stack:** Phase 4 layer 6. Base =
`shew/turbo-5820-migrate-native-task-definition-precedence`.
## Changes
- Add `PackageGraph::resolve_native_task_command` (catalog templates +
which + overrides)
- `ToolchainCommandProvider` plans via that API instead of
`toolchain.task_command`
- Preserve override / pure-native-root / MFE / compile-cache decoration
behavior
## Out of scope
Lazy binary cache polish (TURBO-5822), env/hash contract changes.
## Testing
- `cargo test -p turborepo-task-executor --lib` (18 passed)
- `cargo clippy -p turborepo-repository -p turborepo-task-executor
--all-targets -- -D warnings`
Closes TURBO-5821.
Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Anthony Shew <anthonyshew@users.noreply.github.com>
