feat(org): org build limit types

[alexhholmes-work]

Foundation layer for org-level build limits: constants, platform settings toggle, API and database types, and middleware for default/max limit values.

The EnableOrgBuildLimit platform setting gates the feature. When disabled, enforcement is skipped entirely. The OrgBuildLimit type represents a per-org concurrent build cap with configurable limit, created/updated timestamps, and the modifying user.

Changes

• Add OrgBuildLimitMin (1), OrgBuildLimitMax (100), and OrgBuildLimitDefault (30) constants in constants/limit.go
• Add TableOrgBuildLimit table name constant in constants/table.go
• Add EnableOrgBuildLimit bool field to the Platform settings type with getter/setter, CLI flag (vela-enable-org-build-limit), and FromSettings propagation
• Fix struct tag alignment in api/types/settings/platform.go and database/types/settings.go to satisfy tagalign linter
• Add enable_org_build_limit column to the settings database table schema
• Add OrgBuildLimit API type in api/types/org_build_limit.go with getters, setters, and String() method
• Add OrgBuildLimit database type in database/types/org_build_limit.go with ToAPI() and validation
• Add DefaultOrgBuildLimit and MaxOrgBuildLimit gin middleware for injecting limit bounds into request context
• Add unit tests for all new types and middleware