feat: add Swift/Xcode error and stacktrace compression

[Cyvid7-Darus10]

This adds a new swift subcommand and Swift crash trace compression to contextzip, addressing #1.

If you work on iOS/macOS projects, you know the pain of Xcode build output flooding your terminal. A typical swift build dumps a CompileSwift normal arm64 /path/to/every/single/file.swift line for every source file in your project, followed by linking steps, code signing, and other noise that buries the actual errors you care about. This filter collapses all of that into a one-line summary like swift build: 47 Swift files compiled, 2 targets linked while preserving every error and warning with full file paths and context.

The same goes for Swift crash stack traces. When your app crashes, you get a wall of numbered frames from UIKit, Foundation, libswiftCore, CoreFoundation, and GraphicsServices that are almost never relevant to debugging. This filter hides those framework frames and keeps only your app's frames, so instead of scrolling through 20+ lines of Apple internals, you see your 2-3 app frames with a (+ 15 framework frames hidden) note.

Here is a before/after for a build with errors:

Before (raw Xcode output):

CompileSwift normal arm64 /Users/dev/project/Sources/App.swift
CompileSwift normal arm64 /Users/dev/project/Sources/Models/User.swift
CompileSwift normal arm64 /Users/dev/project/Sources/Views/ContentView.swift
... 47 more lines like this ...
/Users/dev/project/Sources/App.swift:42:15: error: cannot convert value of type 'String' to expected argument type 'Int'
CompileSwift normal arm64 /Users/dev/project/Sources/Utils/Logger.swift
Ld /Users/dev/build/Debug/MyApp normal arm64
** BUILD FAILED **

After (contextzip swift build):

swift build: 50 Swift files compiled, 1 target linked

1 error:
/Users/dev/project/Sources/App.swift:42:15: error: cannot convert value of type 'String' to expected argument type 'Int'
        let x: Int = name
                     ^~~~

** BUILD FAILED **

The implementation follows the exact same patterns as cargo_cmd.rs and dotnet_cmd.rs. It adds swift_cmd.rs with the command handler and filter logic, extends error_cmd.rs to detect and compress Swift crash traces (making it 6 languages instead of 5), and hooks into the runner.rs post-processing pipeline for contextzip err output. All 1062 existing tests continue to pass, and 6 new tests cover the Swift-specific functionality.

Demo