Clean up host related code

[jakebailey]

This removes the need to have options as part of the CompilerHost entirely, and is a cleanup we were thinking about ages ago.

The only notable change is that we now just use \n for the output newline on Windows, which I think is just fine.

Also clean up some other unused code in the host.

[Copilot]

Pull Request Overview

This PR cleans up newline handling by removing the NewLine method and related options from host interfaces, standardizing on "\n" for all outputs, and simplifying compiler host creation signatures.

• Removed all NewLine() methods and fields from host interfaces and implementations.
• Updated calls to compiler.NewCompilerHost (and related helpers) to drop the compiler options argument.
• Switched from sys.NewLine() and fmt.Fprint(…, …, sys.NewLine()) to literal "\n" and fmt.Fprintln where appropriate.

Reviewed Changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
internal/project/host.go	Removed NewLine() from ServiceHost interface
internal/project/project.go	Dropped NewLine() method and interface reference
internal/execute/system.go	Removed NewLine() from System interface
internal/execute/watcher.go	Updated NewCompilerHost calls and replaced newline printing
internal/execute/watch.go	Replaced fmt.Fprint + sys.NewLine() with fmt.Fprintln
internal/api/server.go	Removed NewLine field and NewLine() implementation

Comments suppressed due to low confidence (1)

internal/api/server.go:99

• [nitpick] The newLine field in the Server struct is no longer assigned or used after removing the NewLine method. Consider deleting this field to avoid dead code.

		cwd:                options.Cwd,