feat(railpack): add buildpack control var filtering and dev seeder

Extract NIXPACKS_/RAILPACK_ prefix filtering into a reusable
`scopeWithoutBuildpackControlVariables` query scope on EnvironmentVariable.
Apply scope consistently to runtime vars, runtime preview vars, and
buildtime var generation in ApplicationDeploymentJob.

Refactor `generate_railpack_env_variables` to return a Collection.
Add `RAILPACK_FRONTEND_IMAGE` constant and bake it into the
coolify-helper Dockerfile as a build arg.

Add DevelopmentRailpackExamplesSeeder (dev/local env only) for
seeding example Railpack apps, wired into DatabaseSeeder.

Add tests:
- ApplicationDeploymentControlVarFilteringTest: verifies control vars
  are excluded from runtime and buildtime envs
- DevelopmentRailpackExamplesSeederTest: verifies seeder behavior
- ApplicationDeploymentRailpackEnvParityTest: parity checks for env
  handling across build/runtime paths

openapi.yaml

@@ -2765,8 +2765,8 @@ paths:
                   type: integer
                   description: 'Number of days to retain backups locally'
                 database_backup_retention_max_storage_locally:
-                  type: integer
-                  description: 'Max storage (MB) for local backups'
+                  type: number
+                  description: 'Max storage (GB) for local backups'
                 database_backup_retention_amount_s3:
                   type: integer
                   description: 'Number of backups to retain in S3'
@@ -2774,8 +2774,8 @@ paths:
                   type: integer
                   description: 'Number of days to retain backups in S3'
                 database_backup_retention_max_storage_s3:
-                  type: integer
-                  description: 'Max storage (MB) for S3 backups'
+                  type: number
+                  description: 'Max storage (GB) for S3 backups'
                 timeout:
                   type: integer
                   description: 'Backup job timeout in seconds (min: 60, max: 36000)'
@@ -3160,7 +3160,7 @@ paths:
                   type: integer
                   description: 'Retention days of the backup locally'
                 database_backup_retention_max_storage_locally:
-                  type: integer
+                  type: number
                   description: 'Max storage of the backup locally'
                 database_backup_retention_amount_s3:
                   type: integer
@@ -3169,7 +3169,7 @@ paths:
                   type: integer
                   description: 'Retention days of the backup in s3'
                 database_backup_retention_max_storage_s3:
-                  type: integer
+                  type: number
                   description: 'Max storage of the backup in S3'
                 timeout:
                   type: integer