feat: add pythonlings doctor diagnostics

[Huoyanlifusu]

Closes #46

Summary

Adds pythonlings [--root PATH] doctor, a read-only diagnostic command that reports:

• Python runtime and installed package version
• workspace structure and manifest validity
• solution availability
• progress-state readability
• reset-snapshot coverage
• bundled-docs coverage

Warnings never fail the command; required failures exit 1. The command never
creates, repairs, renames, or otherwise modifies workspace files — it uses its own
non-mutating inspection path (no reuse of the mutating state loader) and mirrors
core/reset.py's snapshot-path logic only.

Behavior

• Discoverable in pythonlings --help and respects global --root (explicit
  --root wins over the current workspace).
• Resolution failures (symlink loops, unknown ~user) are reported as a friendly
  [FAIL] Workspace: line with no traceback.
• Malformed manifests (wrong field types, missing files, directories where files
  belong) are caught and reported as [FAIL] Manifest: with no traceback.
• Corrupt or unreadable state is a warning and is never touched (no .bak, no repair).

Tests

• python -m pytest tests/unit/test_doctor.py tests/integration/test_cli_doctor.py -q
  • 18 passed
• python -m pytest -q
  • 169 passed
• pythonlings --root tests/fixtures/passing_curriculum verify
  • passed
• pythonlings --root tests/fixtures/passing_curriculum doctor
  • 8 checks, 3 warning(s), 0 failure(s) (fixture lacks solutions/snapshots/docs)
• Read-only check on a freshly inited workspace (1172 files): SHA-256 hashes
  identical before and after doctor

Representative output (healthy workspace)

Pythonlings doctor
Workspace: <root>

[OK] Python runtime: Python 3.11.15
[OK] Pythonlings version: pythonlings 0.4.1
[OK] Workspace: <root>
[OK] Manifest: 292 exercises across 31 topics
[OK] Solutions: 292/292 available
[OK] Progress state: no progress file yet
[OK] Reset snapshots: 292/292 available
[OK] Bundled docs: 31/31 topics available

Summary: 8 checks, 0 warning(s), 0 failure(s)

[coderabbitai]

Important

Review available on request

• 🔍 Trigger review

Reviews should be triggered manually for repositories with fewer than 10 stars. Select Trigger review above or comment @coderabbitai review to review the latest changes. For a full review, comment @coderabbitai full review.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: c95687df-8501-4b0c-9fdb-6dbdb9c797ab

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}