feat(tenant): add mode-aware ownership scopes

[KilianBoute]

Summary

• add strict legacy, compatibility, and canonical tenancy modes
• expose mode-aware organisation and organisation/project scope builders
• retain existing helpers as compatibility wrappers
• keep project predicates distributed into ownership arms when safe for index use

Validation

• GOWORK=off go test ./...
• GOWORK=off go vet ./...
• git diff --check

[codecov]

Codecov Report

❌ Patch coverage is 75.51020% with 12 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/database/tenant.go	75.51%	8 Missing and 4 partials ⚠️

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