fix(health): report endpoint diagnostics

[upsetbit]

Summary

• make plane_health probe both states and issues endpoints
• return structured per-endpoint diagnostics, counts, warnings, and ok=false for suspicious/no-state project access
• update the tool description to match the validation depth
• add MCP-level regression coverage for healthy, suspicious empty, and endpoint-error health results

Root Cause

The old health tool treated any successful states response as full project health. That hid cases where project access was partial or suspicious.

Validation

• go test ./internal/mcpserver -run 'TestHealth|TestWorkspaceInfo|TestToolsList' -count=1\n- go test ./... -count=1\n- just lint-sec\n- GOTOOLCHAIN=go1.26.4 go run golang.org/x/vuln/cmd/govulncheck@latest ./...\n\nCloses fix(health): detect unusable project access instead of returning ok for any state response #7