feat: add Kiro as a supported platform

[jindalarpit]

Add Kiro as a supported platform

Summary

Adds Kiro as a fully supported AI coding platform in code-review-graph. Kiro uses .kiro/settings/mcp.json for MCP server configuration (same JSON object format as Claude Code's .mcp.json) and .kiro/steering/*.md for agent instruction files (analogous to CLAUDE.md).

What changed

code_review_graph/skills.py

• Added "kiro" entry to the PLATFORMS dictionary with config path .kiro/settings/mcp.json, mcpServers key, object format, and needs_type=True
• Added workspace-level detection in install_platform_configs(): when target="all", Kiro is included if repo_root/.kiro exists (even if ~/.kiro does not)
• Added ".kiro/steering/code-review-graph.md": ("kiro",) to _PLATFORM_INSTRUCTION_FILES
• Added file_path.parent.mkdir(parents=True, exist_ok=True) in _inject_instructions() to support nested paths like .kiro/steering/

code_review_graph/cli.py

• Added "kiro" to --platform choices on both install and init commands

tests/test_skills.py

• Added TestKiroPlatform class with 9 unit tests covering: PLATFORMS entry validation, MCP config creation, existing server preservation, duplicate prevention, steering file creation, steering idempotency, all-platform detection, workspace-level detection, and dry-run behavior
• Updated two existing assertions in TestInjectPlatformInstructionsFiltering to include the new kiro steering file in the expected set

diagrams/generate_diagrams.py

• Added Kiro to the d8() platform diagram with config path .kiro/settings/mcp.json
• Regenerated .excalidraw file (PNG re-export from excalidraw.com still needed)

README.md

• Added --platform kiro example to Quick Start
• Updated platform lists in image alt text and footer

Detection logic

Condition	Kiro detected?
~/.kiro exists	Yes (via detect lambda)
<repo_root>/.kiro exists	Yes (via workspace-level check in install_platform_configs)
Neither exists	No

How to test

# Run the Kiro-specific tests
pytest tests/test_skills.py::TestKiroPlatform -v

# Run the full suite
pytest tests/ --tb=short -q

# Lint
ruff check code_review_graph/

Usage

code-review-graph install --platform kiro    # configure only Kiro
code-review-graph install                    # auto-detects Kiro if .kiro/ exists

This creates:

• .kiro/settings/mcp.json with the code-review-graph MCP server entry
• .kiro/steering/code-review-graph.md with graph-usage instructions