feat: Implement Knowledge Graph Schema Linter

[AlexMikhalev]

Summary

Implement KG schema linter based on design from closed PR #294.

Design Plan

See .docs/plans/kg-schema-linter-design.md for full design document.

Key Features

1. Validate KG markdown files against schema rules
2. Report lint issues with severity, code, and message
3. JSON output for CI/CD integration
4. Skill integration for agentic loop validation

New Crate Structure

crates/terraphim_kg_linter/
├── Cargo.toml
├── src/lib.rs      # Core linting logic
├── src/main.rs     # CLI binary
└── tests/basic.rs  # Integration tests

CLI Usage

cargo run -p terraphim_kg_linter -- --path docs/src/kg --strict

Implementation Timeline

Phase	Duration	Deliverable
Crate structure, types	1 day	Basic structure
Linter implementation	2 days	Core logic, CLI
Workspace, skill, CI	1 day	Integration

Origin

Extracted from closed PR #294 (85 files, conflicting). Fresh implementation approach.