feat: add teach check — cross-tool validation summary

[Data-Wise]

Quick Win 4: teach check — Cross-Tool Validation Summary

Effort: 2-3 hours | Priority: Medium (unified health view)
Blocked by: Craft QW3 (config normalization) — now complete

Problem

Three validation tools exist but users must know about and run each separately. No unified health view.

What to implement

A teach check subcommand that runs all three validation layers and presents a unified report.

Where

Add check|chk case to teach() function. Create _teach_check() function.

Validation layers

1. Config syntax (flow-cli) — yq '.' "$config_file"
2. Schema validation (Scholar, if available) — _teach_build_command validate
3. Content validation (Craft, if available) — python3 commands/utils/teaching_validation.py
4. Quarto render check (flow-cli) — render/syntax validation

Output design

╭─────────────────────────────────────────────╮
│  TEACHING PROJECT HEALTH                     │
╰─────────────────────────────────────────────╯
  Config syntax      PASS   [flow-cli]
  YAML schema        PASS   [scholar]
  Syllabus sections  PASS   [craft]    4/4 required
  Schedule           WARN   [craft]    week 14 missing content
  Assignments        PASS   [craft]    all referenced files exist
  Quarto render      PASS   [flow-cli]

  5/6 passed, 1 warning

Implementation sketch

_teach_check() {
    local config_file=$(_teach_require_config) || return 1
    local pass=0 warn=0 fail=0 total=0
    # Run each validation layer, aggregate results
    # Gracefully skip unavailable tools (Scholar/Craft)
}

Verification

• teach check shows unified report from all available validators
• Gracefully handles missing Scholar/Craft plugins

Context

Part of the Teaching Ecosystem Coordination spec. Craft-side changes (QW3: config normalization) merged in Data-Wise/craft@ced5ac5 — Craft's content validator now works on real flow-cli configs.