Returns the list of all registered AI cost-intelligence investigators (detectors) available for the insights engine. Each entry includes:

• id — the stable string identifier used in excludeInvestigatorIds when calling POST /insights/runs
• displayName — human-readable label for UI display
• category — the finding category this investigator emits (e.g. retry_waste, outdated_model, error_concentration)
• version — the investigator version string

Use this endpoint to discover valid values for excludeInvestigatorIds before submitting a run. An MCP agent can call this once to build the exclusion list for the runRecommendations tool. The list reflects the investigators currently deployed on the server — check this endpoint rather than relying on hard-coded IDs.