feat: add dcode doctor and dcode update subcommands

[rosstaco]

Summary

Adds two new subcommands to dcode:

• dcode doctor [PATH] — diagnoses the local environment (editor, devcontainer extension, container runtime, git, WSL setup, target devcontainer, dcode version, install method) and prints a "what would dcode <PATH> do" plan summary. Read-only — never patches settings.json or spawns the editor. Exit code: 0 if no failing checks, 1 otherwise. Warnings do not fail.
• dcode update — shells out to uv tool upgrade dcode. Detects when uv is missing or dcode wasn't installed via uv tool and prints actionable hints instead of forwarding the raw error.
• dcode update --check — checks GitHub Releases for a newer version without installing. Exit 0 if up-to-date or ahead (dev build), 1 if behind, 2 on network error.

Output is rendered with rich — colored status glyphs, per-section panels, and a clickable release URL on supporting terminals. Auto-disables color on non-TTY and when NO_COLOR=1.

Commits

#	Type	Subject
1	refactor	split cli into core and wsl modules
2	refactor	split test_cli into test_core, test_wsl, conftest
3	feat	add update subcommand
4	feat	add doctor subcommand
5	docs	document doctor and update subcommands
6	feat	prettify doctor and update output with rich
7	feat	render each doctor section in its own panel

The two refactors land first as pure code-moves so the feature commits read against a clean per-module structure. Each commit passes the full test suite individually.

Module layout (new)

src/dcode/
├── __init__.py        (unchanged)
├── __main__.py        (unchanged)
├── cli.py             (argparse + subcommand dispatch)
├── core.py            (run_dcode, find_devcontainer, resolve_worktree, build_uri, …)
├── wsl.py             (is_wsl, build_uri_wsl, settings.json patcher, …)
├── doctor.py          (NEW — 13 checks + plan-summary + driver)
├── update.py          (NEW — uv tool detection + upgrade + --check)
├── version_check.py   (NEW — GitHub Releases API, version comparator)
└── _rich.py           (NEW — Console singleton + status-glyph styles)

New runtime dependency

• rich >= 13.0 (added to pyproject.toml). Pure-Python, widely used. Auto-disables color on non-TTY / NO_COLOR.

No other new deps. The GitHub API call uses stdlib urllib.request.

Tests

• Baseline: 39 tests
• After this PR: 156 tests (+117)
• All checks return (status, message, hint) tuples → 95% of doctor tests assert on the data, not the rendering, so they're robust against future UI changes.
• No real network or subprocess in the suite — everything mocked via unittest.mock.patch against urllib.request.urlopen, subprocess.run, shutil.which.
• Two new tests assert that NO_COLOR=1 produces zero ANSI escape sequences in doctor and update --check.

Verification on this machine

• uv run pytest -q → 156 passed
• uv run ruff check → All checks passed!
• python -m dcode doctor → 7 ok / 2 warn / 0 fail (only code-insiders and the absent .devcontainer/ warn — both expected on this repo). Plan-summary prints. Exit 0.
• python -m dcode doctor /tmp → confirms [PATH] argument routes correctly.
• python -m dcode update --check → correctly reports the local hatch-vcs dev version as ahead of v0.4.2 (the dev-build vs released-version case is covered explicitly in the version comparator and unit-tested).

Release-please / version bump

Multiple feat: commits → release-please should propose a minor bump from 0.4.2 → 0.5.0. Conventional Commit messages are intact for changelog generation.

Notable design choices

• Per-check functions return tuples, not direct prints. The renderer is the only thing that touches stderr, which made the 53 doctor tests trivial and decoupled rendering from logic.
• argparse subcommand routing — Python 3.13 argparse misparses dcode ./somepath as an invalid subcommand when subparsers are mixed with a top-level positional. Solved with a _looks_like_subcommand peek over sys.argv[1:] against a _SUBCOMMANDS = ("update", "doctor") tuple. The escape hatch dcode ./doctor (open a folder literally named doctor) works as documented in the README.
• doctor is read-only — even on WSL, where the existing dcode <path> flow auto-patches settings.json, doctor only reports what would change.
• Plan-summary smart editor fallback — if only code-insiders is installed, the plan replays as dcode -i instead of the default dcode path. If neither editor exists, the plan-summary section says "no editor available" and is omitted from the exit-code calculation.

Acceptance against the original plan

All criteria from project/plans/2026-04-29-doctor-update/plan.md §10 satisfied. Real-output excerpts captured in project/plans/2026-04-29-doctor-update/implementation-notes.md under "Commit 3/4 validation" and "Rich UI validation" sections.