Add hc-run resource handler

[binrogithub]

Motivation

• Introduce a read-only resource handler to resolve hc-run://<run_id>/<artifact> URIs into artifact content for MCP integration.
• Ensure artifact access is safe and deterministic by validating and normalizing artifact paths and preventing path traversal.
• Provide sanitized outputs for markdown and JSON artifacts so downstream consumers receive predictable content_type and body values.

Description

• Add new package scaffolding hc_agent with hc_agent/mcp/resources.py that implements HcRunResourceHandler, a minimal RunStore protocol, and handle_hc_run_resource convenience wrapper.
• Implement parse_hc_run_uri to validate hc-run URIs, require a run id, forbid params/query/fragment, and block path traversal or unsafe characters.
• Provide _build_response that returns text/markdown; charset=utf-8 for .md/.markdown and validates/parses JSON for .json, reserializing it with json.dumps(..., ensure_ascii=False, separators=(",",":")) to sanitize output.
• Define explicit error types InvalidResourceUri, ResourceNotFound, and UnsupportedArtifactType and remove NULs from text and decode bytes with UTF-8 errors="replace" for robustness.

Testing

• No automated tests were executed against the new handler as part of this change.
• Files were created and committed (hc_agent/__init__.py, hc_agent/mcp/__init__.py, hc_agent/mcp/resources.py) and basic file presence was inspected successfully.

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Codex Task