feat(cli): support external workspace paths

[Yell-walkalone]

What Changed

• Add optional --path handling for ecc run so a workspace can live outside the project directory; without it, the existing project-local workspace layout remains unchanged.
• Add ecc workspace import WORKSPACE --project PROJECT --path PATH to register an existing external workspace without opening or changing it.
• Persist canonical external workspace paths in the project manifest, validate conflicts and existing registrations, and document the CLI behavior in English and Chinese user guides.

Scope

• CLI - command behavior, Typer command surface, output formats, or workspace commands.
• Flow/runtime - workspace lifecycle, EngineFlow, step execution, logs, metrics, or artifacts.
• EDA integration - Yosys, ECC-Tools, DreamPlace, KLayout, PDKs, or native/runtime wrappers.
• Build/package - Nix, PyInstaller, wheels, uv.lock, or release artifacts.
• CI/release - GitHub Actions, version checks, changelog, or release automation.
• Tests/docs only

Runtime And Packaging Impact

• CLI output or machine-readable contract changed
• Workspace layout, flow state, or artifact paths changed
• No native toolchain or dependency changes
• PyInstaller, Nix, or release artifact changed

Notes:

• The default workspace path behavior is unchanged when --path is omitted.
• No generated build output or package artifact is committed.

Validation

• uv run --no-sync ruff format --check chipcompiler test
• uv run --no-sync ruff check --output-format=github chipcompiler test
• Targeted workspace-path/manifest tests: 54 passed
• PyInstaller build and smoke: ECOS_PYINSTALLER_MODE=onedir uv run --no-sync --managed-python pyinstaller ecc.spec --clean --noconfirm; ecc --version, ecc run --help, and ecc workspace import --help passed.
• Manual GCD CLI check with /nfs/home/huangzengrong/projects/benchmark/gcd: external ecc run --path --resume returned no_op=True, and ecc workspace import --path registered successfully; manifest paths matched the requested directories. No flow steps were run.
• nix run .#cli -- --help (not run; unrelated to this CLI change)

Skipped checks and reason:

• Full pytest command was run. 2,765 tests passed, 6 skipped, and 4 xfailed; 34 existing filesystem-sensitive tests failed only when their temporary directories were on the repository NFS mount (renameat2(RENAME_EXCHANGE) returned EINVAL, and one cleanup assertion observed an NFS .nfs* file). The same affected tests pass with --basetemp=/tmp except the existing test that requires a complete PDK unavailable in this local fixture environment.
• The built build/ and dist/ directories were removed before publishing.

Checklist

• I kept the change scoped to ECC.
• I updated docs or user-facing CLI text where behavior changed.
• I included lockfile or version metadata updates when dependencies changed.
• I documented skipped validation and remaining risk.
• I did not include local caches, virtual environments, or generated build outputs.
• No Co-authored-by trailer was added.