fix[backend](datasources): added datasources tenant verification

[AlexSanchez-bit]

No description provided.

[github-actions]

✅ AI review — Clean

No issues detected in this diff.

✅ architecture (gemini-3-flash-lite) — clean

Summary: Fixes multi-tenancy leakage in datasources by adding tenancy checks, cross-tenant group validation, and cascade clearance on group deletion.

No findings.

✅ bugs (gemini-3-flash-lite) — clean

Summary: No concrete bugs found. The diff correctly wires tenant-scoped group lookups and clears dangling foreign keys on deletion.

No findings.

✅ security (gemini-3-flash-lite) — clean

Summary: PR adds multi-tenancy validation for datasource groups, cleans up dangling references on delete, and includes unit tests.

No findings.

🔴 go-deps — pending updates

🔍 Discovered 29 Go projects

❌ Could not inspect the following projects (run 'go mod tidy' there):

## ./plugins/alerts
go: github.com/threatwinds/go-sdk@v1.1.27-0.20260804160110-0dab0e82abf5 (replaced by /Users/yorjanderhernandez/code/threatwinds/go-sdk): reading /Users/yorjanderhernandez/code/threatwinds/go-sdk/go.mod: open /Users/yorjanderhernandez/code/threatwinds/go-sdk/go.mod: no such file or directory