feat(cli): add --cwd DIR to run against another project (closes #69)

[dchaudhari7177]

Closes #69.

What

gcode --cwd DIR, the equivalent of git -C:

gcode --cwd /some/project

The banner shows /some/project, .gcoderc is read from there, and every tool resolves paths against it.

The ordering is the whole feature

The chdir runs immediately after parse_args, before load_env(). That placement is what makes the acceptance criteria hold: .gcoderc discovery (load_config(project_root=os.getcwd())), ui.banner(..., os.getcwd()) and all the tools resolve against the working directory. A chdir performed any later leaves them describing different projects within one session — config from the launch directory, tools operating in the target.

So rather than assert the banner text, the test observes the working directory from inside load_env — the first call after the chdir — which pins the ordering directly:

monkeypatch.setattr("gcode.cli.load_env", _record)   # records cwd, then raises

Errors

A bad --cwd goes through parser.error(): one line on stderr, exit 2, no traceback — the same treatment as other bad input. OSError covers both a missing directory and a path that turns out to be a file, and the message carries strerror so the two are distinguishable:

gcode: error: --cwd '/no/such/project' is not usable: No such file or directory

Tests

Five in tests/test_cli.py:

• --help lists the flag
• the chdir is observed from load_env, proving it precedes config loading
• without the flag the directory is untouched
• a missing directory exits 2 with no traceback
• a path that is a file exits 2

Each restores the original cwd in a finally, so a failure can't leak into later tests. Two fail on main (checked by stashing only gcode/cli.py).

Verification

pytest tests/test_cli.py — 15 passed. ruff check clean.

Full suite on this branch: 57 passed, 2 failed — the 2 are test_tools.py::test_grep / ::test_grep_ignore_case, which fail on a Windows checkout of main for an unrelated reason, sent separately as #78.

The issue mentions load_config(project_root=...) from #48; that already exists on main and needed no change, since it reads os.getcwd() at call time.