feat: Scholar Config Sync wiring + new teach wrappers

[Data-Wise]

Summary

Wire flow-cli's existing config infrastructure to Scholar's --config flag and add new teach subcommands wrapping Scholar features.

From: #299 (Scholar side complete), SPEC-scholar-config-sync-2026-02-26.md

Scope

Core Wiring

• Auto-inject --config .flow/teach-config.yml on all Scholar commands
• Wire _teach_find_config() into command assembly block
• Wire _flow_config_changed() for stale config warnings
• Legacy deprecation warning for .claude/teaching-style.local.md

New Config Subcommands

• teach config check — validate config (maps to /teaching:config validate --strict)
• teach config diff — compare prompts vs defaults
• teach config show — show resolved 4-layer config
• teach config scaffold — copy default prompts for customization

New Scholar Wrappers

• teach solution — generate standalone solution keys
• teach sync — sync config to Scholar format
• teach validate-r — validate R code in .qmd files

Doctor Integration

• Config sync status section in teach doctor

Documentation

• Help output updates
• MASTER-DISPATCHER-GUIDE updates
• TEACHING-SYSTEM-ARCHITECTURE updates
• New SCHOLAR-INTEGRATION-GUIDE.md

Spec

docs/specs/SPEC-scholar-config-sync-2026-02-26.md — 7 increments, ~3-4 hours

Prerequisites

• Scholar plugin v2.2.0+ (installed)
• feat: Teaching config consolidation - unified config for flow-cli and Scholar #298 teach migrate-config (complete)